What if I don't have any of the old computers that I had previously authorized for Itunes

Use the Deauthorize All button in the screenshot below from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support and then authorize any computers you still want to use:

See how many computers are authorized

1. Open the Apple Music app or Apple TV app.
2. Choose Account > Account Settings.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. At the top of your Account Information page, look next to Computer Authorizations to see how many computers are authorized.
5. 

If you need to deauthorize a computer that you don't have access to

To deauthorize a computer that you don't have access to, you have to deauthorize all of your computers. Then authorize each computer that you have again. You can deauthorize all computers only once a year.

1. Open the Apple Music app or Apple TV app.
2. Choose Account > Account Settings.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. At the top of your Account Information page, go to the Apple ID Summary section.
5. Next to Computer Authorizations, click Deauthorize All.
6. Authorize each computer that you use again.