iTunes asking to set up as new device but it's already done.
My son has inherited my wife's old iPhone SE and we've set him & it up on iCloud as a family member and everything's running fine. But... I've just connected his phone to my iMac to back it up and iTunes is asking me to either set up the phone as a new handset or to restore from one of my wife's old backups. How do I get round this? I don't want to restore his phone.
iPhone SE