- You may be looking for Fal-tor-voh.
This ritual was performed on Captain Spock in 2285 after he was recovered from the Genesis Planet by Admiral Kirk. Prior to Spock's death during the Battle of the Mutara Nebula, he had transferred his katra into Doctor Leonard McCoy, but after the Genesis effect revived Spock's body, the Enterprise senior staff took McCoy and the resurrected Spock to Vulcan, where Sarek requested that fal-tor-pan be performed to restore Spock's katra to his body.
The ritual was considered very dangerous, both to the recovering deceased person, and to the keeper of the katra. For this reason, it was almost never performed, and at the time of Spock's fal-tor-pan, it was unclear whether the ritual had ever been performed at all. (Star Trek III: The Search for Spock) Despite the implied danger, McCoy came through the ritual unharmed, and, after a period of temporary amnesia as his knowledge returned to him, Spock soon returned to himself.