accessing a second hand watch i bought that has the password

You don't, the best option is to return it. The Watch is Activation Locked to prevent use by anyone else, unless the original owner removes it from their account. This is what the original owner needs to do before selling:

https://support.apple.com/en-us/102542

If you could simply reset it and use the Watch, then that means someone else could steal your Watch and do the same thing. Fortunately that is not the case, and something else you should be aware of is that the person who used the watch previously can still track it using Find My, so they know exactly where it is.

zalanda wrote:

i bought a second hand apple watch and when i charged it, it has a pssword. how can i fully reset the watch and pair onto my device?

Contact the person you bought the watch from to get the password, if you can't get it return it, and if you can't do that recycle it, the watch is useless.