How to deauthorize a device on Apple Music

I am currently trying to add a new MacBook to my Apple Music library. It tells me to go to Account Settings and deauthorize other computers but when I go to account settings it doesn't list the other computers, it just says "one machine is authorized to play content purchased with this account."

How can I deauthorize other machines when I can't see which ones they are?

[Re-Titled by Moderator]