How do I erase my Apple ID from an old iPhone 14 Pro I gave to a friend?

I have upgraded to 15 from 14 pro and handed my old phone to friend. He was using old IPhone 14 Pro with his new Apple ID. Suddenly, after 2 months, He cant use his apple ID on apple store instead it is cont suggesting my Apple ID and saying to give my Apple ID Password. He is complaining me to solve the issue. How to solve his issue???

[Re-Titled by Moderator]