See above.
Hard to say when we don't know what you have tried.
Make sure you got the correct country setting in your Garmin Account: https://www.garmin.com/account/profile (it affects pairing of some watches so best to check that it is correct)
Check that the watch is removed from Garmin Connect AND bluetooth devices in the phone. Restart both phone and watch. Make sure you've allowed ALL permissions to the Connect app.
After that follow the pairing instruction exactly: Pairing Your Phone with Your Watch