1. Go to appleid.apple.com
2. Log in using your Apple ID and password.
3. Scroll down to "Devices."
4. Click on the name of the Macbook Pro.
5. A small window will open; click on "Remove."

You may also want to read Apple's advice on [What to do before you sell or give away your Mac][1].


  [1]: https://support.apple.com/en-us/HT201065