Correct passcode doesn't work
Typed in only passcode ever used, doesn't work
Apple Watch Series 2
You will have to race to watch and start over hopefully from my back up. If there is an Apple ID set up correctly it will have an activation lock on it and setting it up will also require the Apple ID password on the watch.
While they watch is on the charger, hold down the power button until you see the option to slide off, but do not turn off. Instead force touch the display( press hard )until you see the option to erase reset.