delete contacts on old iPhone 6
I upgraded recently to an iPhone 13 pro from an iPhone 6. I want to return the iPhone 6 to Verizon for credit without my personal information. currently my iPhone 6 and 13 pro seem to be sharing data. If I delete a contact on my iPhone 6 it also deletes the same contact on my iPhone 13 pro.
Is there a setting so the iPhone 6 can be unpaired or disconnected from my iPhone 13 pro and MAC so I can only delete contacts on the iPhone 6?
iPhone 6, iOS 12