Unsync and Wipe old iPhone without affecting new iPhone
I was given an iPhone 11 (iOS 17.4.1) still signed in to the donor's account and synchronized with their new iPhone 15 Pro (iOS 17.4.1). How do I terminate the synchronization between the two phones and safely wipe my iPhone 11 without simultaneously wiping or affecting any data on the donor's new iPhone 15 Pro?
iPhone 11