Highlights

The connection to past Avatar lives is crucial for the Avatar to have wisdom, experience, and power to protect and bring peace to the world.
Aang reconnected with his past Avatars through intentional methods like meditation and triggering shared memories.
The next Avatar could potentially restore the past lives through spiritual means, such as spiritbending or triggering past Avatar consciousness through meditation or shared memories, leading to a deeper exploration of the Avatar's inner peace and power.

It is presumed that after Korra's battle with Unalaq, in The Legend of Korra, she lost her connection to the past Avatar lives introduced in Avatar: The Last Airbender . However, there may be a way to restore the Avatar's past lives, and the original series may have alluded to the solution. Avatar Aang was a deeply spiritual Avatar who could connect with spirits and his past lives with relative ease.

The connection to past lives is important for several reasons. It provides the Avatar with the acculmulated wisdom, experience, and power to be a more impactful bender whose role is to responsibly use that power to protect people and pursue peace. Avatar: The Last Airbender chronicled Aang's disconnection from his Avatar State which can give some insight on how the next Avatar could restore the past lives.

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How Aang Reconnected With Past Avatars

Avatar Aang had various means of connecting and communing with his past Avatar lives. Some methods were intentional and some were by chance. His more intentional methods were through meditating or connecting with a shared memory or object that triggered the consciousness of the past Avatar. For instance, Aang wearing bisexual Avatar Kyoshi's clothes triggered her consciousness to take over where she confesses to killing Chin the Conqueror after creating Kyoshi Island to keep her people safe from invaders. Granted, this trial scene in Avatar: The Last Airbender was more intentional on the part of Katara who planned the hopeful trigger attempt. Still, before face Fire Lord Ozai, Aang meditates to commune with Avatar Roku who tells him:

"All the past Avatars, all their experience and wisdom is available to you."

Even after Aang was disconnected from activating his Avatar State, he was still able to have this connection to his past lives to converse with them for wisdom and guidance at least. This was possible because his Avatar spirit, Raava was still within him. It was Aang's blocked chakras that were preventing him from accessing his Avatar State. But the physical trauma of Aang's back scar, which the blue flames firebender Azula gifted him, hitting a sharp rock in his fight with Ozai reconnected him to his Avatar State. In other words, Azula's lightning strike severed Aang from the Avatar State and a likely equally painful blunt trauma repaired the disconnection.

Avatar Korra, however, lost her connection to the past lives of the Avatars not when Raava was removed from her, but when Raava was being attacked by the dark energy. Avatar Korra's vision of past Avatars disappearing with every blow is similar to the vision Avatar Aang had after hitting that sharp rock. He saw the past Avatars reappear in their Avatar State. This could mean that the vision of Korra seeing the past Avatars disappear may not be a permanent disconnection.

How The Next Avatar Could Restore Past Lives

The next Avatar's connection to spirits may be able to restore the connection to past Avatar lives in similar ways Aang was able to connect to the past Avatars. This assumes that the spiritual connection to the Avatars is still within Raava. It's just temporarily inaccessible due to the dark energy trauma. This brings up another possible solution: spiritbending to heal and purge Raava of the negative effects from any residual dark energy. Whether that's done in a nonviolent way or in an equally physically traumatizing way, albeit still harmless to Raava, healing spiritbending performed on the Avatar would be interesting as it may require a non-elemental bender to learn the art form. That would be a first for the franchise, a natural-born spiritbender. But the methods that Aang used may be useful as well.

Raava is one with the spirits of the Avatars so their past lives are most likely not lost entirely, rather suppressed. If the next Avatar, in their quest for balance, were to focus deep within themself to reconnect with those past lives through meditation or some other method, they may be restored. Also, wearing, for instance, an Avatar's clothes as Aang did, or being in a place that holds a shared memory Raava and a past Avatar have could trigger that Avatar's spirit to resurface. This would allow that Avatar's wisdom, experience, and power to once again become accessible to the next Avatar. It would be a different yet exciting storyline for the franchise if pursued that could even dramatize the next Avatar's inability to control the random manifestations of their past lives as they try to resolve conflicts.

Instead of focusing solely on the world conflicts that the Avatar has to strike a balance to secure peace, the next Avatar: The Last Airbender story could try to find the balance within the Avatar. In a world where benders are becoming increasingly more powerful, many of whom can challenge the Avatar, the next Avatar may desperately need that shared wisdom, experience, and power that the past Avatars could provide in order to maintain peace and a balance of power. An Avatar State that has a short line of accessible Avatars, could force the next Avatar to seek ways to restore as many past lives as possible to learn to be a wiser and stronger Avatar. This would give the series and fans the opportunity to delve deeper into the history and lives of past Avatars as the potential next Avatar seeks to restore inner peace in order to create outer peace.