how can I remove my old MacBook from my apple account

See the "Remove a device from the list" section of Check your Apple ID device list to see where you're signed in - Apple Support

or if you still have the MacBook and are disposing of it, see: What to do before you sell, give away, or trade in your Mac - Apple Support

Kalliath wrote:

how can I remove my old MacBook from my apple account?

please read these references

What to do before you sell, give away, or trade in your - Apple ...

See and remove your devices that are associated with Apple ID purchases

Depending on your macOS, you may have in System Preferences:

>System Preferences>Apple ID> select your device and use the Remove From Account