I bought it from some dude but it’s locked

Activation Lock is designed to prevent anyone else from using an Apple Watch if it's ever lost or stolen.

About Activation Lock on your Apple Watch - Apple Support

Activation Lock is an anti-theft feature that cannot be bypassed. Only the previous owner can remove the lock by using their Apple ID & password. Apple will not help you find the previous owner. If the previous owner cannot or will not remove the lock, then the watch is useless to you or anyone else. Try to get a refund (through eBay) or dispose of the watch properly. In the future, see the 'Before you buy a watch from a third-party' section in:

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support

If you can't get your money back, recycle the watch responsibly. It's totally, utterly useless to you. Apple will NOT help you. We cannot help you.

In addition to everything posted above, read this --> https://discussions.apple.com/docs/DOC-250001038

d4shiesty wrote:

I bought a watch from a random dude but it’s locked

Then you lost your money as that watch is useless can't be unlocked without the original owners information.