Locked watch

I was going to give my Apple Watch to my sister so I unpaired it from my phone. When I turned on my watch, it said device locked, unlock iPhone to start using Apple Watch. I can’t do that anymore though because they aren’t paired. I saw somewhere to hold down on the power off and it would give me an option to erase all content and settings. I tried that several times but it just goes back to the same locked screen. Any advise?