kurtis54 Said:
"Apple Watch series 3: I bought a Apple Watch 2nd hand it was already in set up mode when I got it, but trying to set it up, says it needs the old owned iPhone it was paired to but the person traded the iPhone in for an android and I don’t have their contact info anymore. Is there a way to reset it?"
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No. You must contact the seller, requesting a return. Without that phone, nothing can be done on your end. This is the site the seller should have used prior to selling it to you: What to do Before you Sell, Give Away, or Trade In your Apple Watch, or Buy One from Someone Else - Apple Support. The seller should have known better.