watch

On a computer, go to iCloud.com and sign in with your Apple ID.

Go to Find Iphone.

Select All Devices, then click your Apple Watch.

Click Erase Apple Watch.

Select Next until the device is erased.

Click the remove button next to your Apple Watch.

Then re-pair the watch again.

Where in these steps:

Reset the passcode on your Apple Watch - Apple Support

does it fail? Any error messages? Did you try directly on your watch or on your iPhone? See the above link for instructions for both. Try the other one, if one method fails.

Just to be clear, you mean the watch passcode and not the Apple ID password - correct?