How can I switch the user credentials on my wife’s iPhone 12 Mini from my Apple ID credentials to her different Apple ID and password credentials and still retain all the photos, contacts, and messages that are on her iPhone 12 Mini?

            How can I switch the user credentials  on my wife’s iPhone 12 Mini from my Apple ID credentials to her different Apple ID and password credentials and still retain all the photos, contacts, and messages that are on her iPhone 12 Mini?

Please

tell me the step by step settings procedure I must follow on her Mini to

accomplish this. My wife and I both want me to do this. I know her Apple ID and

password, and also use her Mini.

Additional facts:

 My wife and I each have unique Apple IDs and

passwords. In December 2020, I bought her a new iPhone12 Mini, and by mistake I

set the Mini up with my Apple ID/password. Since then, she has added

many photos, contacts, and messages.

            We do not want to back up the Mini to my iCloud, under my Apple ID/password, which contains my iPhone 5s photos and contacts, because we do not want to merge and share the contacts,

photos, etc., on both devices. My iCloud lists the Mini as a device, but does not contain any photos, contacts or messages from the Mini. I plan to remove the Mini as a device listed on my iCloud.

Thanks in advance.