How do I deauthorize all computers?

See the following from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support

Deauthorize a computer

1. On a Mac, open the Music app, Apple TV app, or Apple Books app. On a PC, open iTunes for Windows.
2. From the menu bar at the top of your computer screen, choose Account > Authorizations > Deauthorize This Computer.
3. Sign in with your Apple ID.
4. Choose Deauthorize.

If you run out of authorizations, deauthorize all

If one of your 5 authorizations is on a computer

that you don't use anymore, deauthorize it. If you sold or gave away a

computer that's used one of your 5 authorizations, you need to

choose Deauthorize All on the Account Information page. Then authorize

each computer that you still use.