Waiting for 90 days with the Music app

A few weeks ago I took over my son's iPhone 7 Plus. Since that time I can't play any music from the music app anymore. When I try to I get a pop-up that the phone is connected to another Apple account and that I can change that but that I have to wait 90 days.

My son checked his account but the iPhone is not connected to his account.

Can someone explain to me what this means or how I can solve this problem?

With regards

Tom