Within Star Wars: The Rise of Skywalker, Rey (Daisy Ridley) utilizes a new force power in Star Wars canon called Force healing, a long forgotten power in which a Jedi can use the Force to heal another by transferring some of their own life energy over to the wounded. While Force healing is mainly used by Rey throughout The Rise of Skywalker, to heal both a sand worm on the planet of Pasaana and Kylo Ren (Adam Driver) after their duel on Kef Bir, Kylo Ren himself also uses this power to bring Rey back to life during the Battle of Exegol - but how did Kylo Ren learn this power?
The Force power heavily featured within The Rise of Skywalker was initially controversial because it introduced discrepancies into past Star Wars adaptations. Rey, a novice Jedi Knight, was able to Force heal when other high-ranking Jedi had no knowledge of this power, including Anakin Skywalker (Hayden Christensen), who’d been searching for this exact type of knowledge to save his wife Padmé from dying during childbirth in Star Wars: Episode III - Revenge of the Sith. The Rise of Skywalker novelization accounts for this inconsistency by explaining that Rey discovered Force heal during her studies of ancient Jedi texts, knowledge that was lost to the passage of time. Unlike Rey, Kylo Ren has not conducted prior research in Force healing, but is still able to heal Rey after she’s killed by Emperor Palpatine (Ian McDiarmid). While it's never directly addressed within The Rise of Skywalker, the mystery behind Kylo Ren’s newly acquired skill could be due to the dyadic Force bond between him and Rey.
Within Star Wars canon, a Force Dyad is when two force-sensitive individuals establish such a strong Force bond that they are one within the Force despite being two different entities. Because their bond is so powerful, it allows those individuals to be both physically and mentally interlinked across space and time. As early as Star Wars: The Force Awakens, Kylo Ren senses his Force bond with Rey when he telepathically invades her mind and states, “Don’t be afraid. I feel it too.” Their dyadic bond is explored even further in Star Wars: The Last Jedi when both Rey and Kylo Ren are able to see and speak to one another despite being light-years apart, as well as experience an increase in power when they fight together against the Elite Praetorian Guards at the end of The Last Jedi.
Since their Force Dyad connection links both of their minds, it’s possible that Kylo Ren was able to access Rey’s knowledge of Force healing. While Kylo never read the Jedi texts personally, it’s possible their mental link through the Force bestowed Rey's own knowledge upon him. Not only does their Force Dyad bond connect Kylo Ren and Rey mentally, but it also allows them to grow stronger with the Force the more they are together. With this in mind, when Rey heals Kylo Ren using the Force on Kef Bir, the simple act of Ren being in Rey’s presence as she is Force healing may have allowed him to acquire the same ability.
Kylo Ren’s Force healing may also be due to another theory that has a correlation to experience. The only other Force-sensitive being who has force healed within Star Wars canon is The Child, better known as “Baby Yoda,” from Disney+’s The Mandalorian, in which The Child heals Greef Carga within the episode “Chapter 7: The Reckoning.” Since Baby Yoda has the appearance and mentality of an infant despite being 50 years old, he clearly hasn’t studied the Jedi texts Rey read herself and almost seems to force heal innately. When Rey heals Kylo, not only does his lightsaber wound heal, but the scar on his face and his psychological damage that caused his inner struggle between the light and dark side of the Force appears to be healed as well, which was in large part helped by Leia sacrificing herself for Kylo.
With this in mind, Kylo Ren may have acquired the ability to Force heal in a similar manner to Baby Yoda, since both of their minds are unpolluted by trauma and experience at the point in time when they Force heal. Since meditation is the key to force healing, the clarity of mind and self which Kylo Ren attains by the end of Star Wars: The Rise of Skywalker allows him to Force heal his Force Dyad partner back to life.