Apple watch 7, activation locked.

Hi there,

I purchased a Series 7 apple watch yesterday and when buying it, I turned it on etc and checked it was reset and working. Everything looked good, was boxed, great condition and charged and reset.

Got home and gave to my partner and when she tried to pair it to her iPhone it stated its locked to an account.

I'm hoping the seller will respond to me and remove it from their account but if they don't... Is there anything I can do?

Regards.