How do I reset the passcode to my Apple Watch?

I have an old Apple Watch Series 3 that I haven’t used for some time.

I have charged it up and tried to open it, but forgot the passcode 🤦🏽‍♀️ I’ve now reached the limit of attempts.

I then have tried to reset via my watch app. However, the series 3 is not showing on my app so I can’t reset it through there or pair it as it is locked. I did change phones since using the old watch so I’m not sure if this is where it has dropped off.

I also now have a series 7 that I use.

Both watches are still showing on my Apple ID account but through there I can only remove the watch and not reset it.

Is there anyway to get into the watch now? Please help? 🙏

[Re-Titled by Moderator]