My Apple Watch had already been paired with my phone, but a couple months ago it just unpaired and I can’t fix it. Any ideas how to fix?

Try restarting your Apple Watch first, then repair according to these instructions - Set up and pair your Apple Watch with iPhone - Apple Support

If that won't work, you may have to erase it and re-pair from there - Unpair and erase your Apple Watch - Apple Support

Some Things to Note

• Your iPhone automatically makes a backup of the Apple Watch when you erase it, so you can set it up again from your backup
• If your Apple Watch is a Cellular model, make sure to keep your cellular plan

Then, you can re-pair it - Set up your Apple Watch - Apple Support

Make sure to select "Restore from Backup" when doing so.

Hope that helped!