I have exceeded my Apple Music limit

Only 5 computers with your Apple ID can play Apple Music. You can deauthorize a computer if you have access to it, but if you do not have access anymore to a computer, then all you can do is use the option to Deauthorize All. There is no list of computers authorized that you can choose individually which one you want removed. If you need to Deauthorize All computer, then you just Authorize the computers that you again want to use for Apple Music. This is only computers that count in the limit, iPhones or iPads do not count.

Authorize or deauthorize your computer for Apple ID purchases - Apple Support