The Confessional is a mechanic in Persona 5.
The confessional can be found in Kanda Church. The protagonist will be able to bring a party member, and by having them confess their guilts in the private booth, they'll be given the ability and option to relearn one old skill. If the protagonist brings someone to the confessional, time will pass.
It should be noted that all of a character's Personas share the same list of skills, so it doesn't matter how different evolutions interact with one another within the system. The only exception is the special skill given to second-tier Personas when the Confidant of their user is maxed out.
The protagonist is unable to bring Morgana to the confessional with Mercurius, as he's only able to be used in December 24, a day when the protagonist can't partake in daily activities. In Persona 5 Royal, the next time Morgana is able to participate in battle is when his Persona has evolved into Diego. The same applies for Goro Akechi and his third-tier Persona, as this awakening only occurs after the calling card for the new Palace is sent.
- If Morgana is brought to the confessional, the protagonist will come inside to translate for him.