Apple watch 3 will not turn on or off

I'm confused with your question, but I want to try and help you.

You say that it won't "turn on or off".

I'd like to see if I can help you get it to turn on first.

The article above offered some suggestions (If your Apple Watch won't charge or it won't turn on - Apple Support)

I am curious:

1. Have you tried another USB wall charger? Just to make sure that there isn't a problem with the one you've been trying. You can take the cord and plug it into a USB port on a computer.

2 I don't know how long you've had your watch, please humor me... Are you attaching the watch to the right side of the charger? The correct side will magnetically 'snap' onto the back of the watch.

3 If the watch is really dead, it'll take it a few minutes before it will have enough charge to begin to light up (the charging icon at least).

Try these things and then please report back with more details about what you've tried.

Hopefully this will get it going.

Hmm... Try reading

Restart your Apple Watch - Apple Support

This screenshot came from there