anyone know how to reset apple watch to factory settings?

If it's a cellular model, the unpair asks whether to keep or remove the mobile plan. Remove it if you're selling, and you may still need to tell your carrier, otherwise you keep paying for it. And don't take the watch off the charger halfway through. It's slow.

Do it from the iPhone if you still have it. Watch app > All Watches > tap the i next to the watch > Unpair Apple Watch. That backs it up to the phone first, wipes it, and turns off Activation Lock. Without the phone you can do it on the watch itself under Settings > General > Reset > Erase All Content and Settings, but Activation Lock stays on. Fine if you're keeping it, a problem if you're selling it, because the next owner can't set it up until you remove it from your Apple ID.