I bought an Apple Watch from a pawn shop and can’t activate it because it didn’t belong to me

Get a refund.

Only the original owner who activation locked it can unlock it.

Apple can't help.

Return it to the pawnshop as you can NEVER use this watch. It is Activation Locked, which you can't unlock and Apple won't unlock for you either.

If you can't get your money back (some places have all sales final policies), you've purchased a useless watch and it should be recycled responsibly.

Read this too --> https://discussions.apple.com/docs/DOC-250001038