Apple Store ID is grayed out and cannot be changed

APPLE STORE ID is grayed out and cannot be changed to the correct one. This happens because my iphone 15 was purchased by my son, who then handed it over to me after like one month. Ever since, the APPLE STORE (not app store) asks for his log in. I cannot change the log in name that displays his email because it's grayed out. The thing becomes more annoying because i bought today an apple watch and it ALSO asks me to log in to apple store with that ID. I tried apple help and could not figure it out. Isn't it so not right that expensive equipment like this gets stuck in what seems really a minor issue? for what reason the log in name in the APPLE STORE is grayed out? why does my apple watch ask me to log in to the APPLE STORE with my son's email and not my correct account emails? very very disappointing of this apple that goes around showing their products are so seamless.