Given old Iphone to aunt

See How to create a new Apple ID https://support.apple.com/en-us/HT204316and

How to switch Apple IDs on your iPhone or iPad

https://www.imore.com/how-change-apple-id-your-iphone-or-ipad

See the data implications below.

Some of these things may apply even though not changing an Apple ID: What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

 Keep in mind that some things available under a first Apple ID will not be available under a new Apple ID. For example, you won’t be able to transfer anything purchased from the App and iTunes Stores to the new ID. And, there are other issues to be addressed.

And see what Eric Root says on this matter here  https://discussions.apple.com/thread/251483565and

what Winston Churchill says about it here: https://discussions.apple.com/thread/7452747

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You also can set up family sharing between the IDs to share purchases made with them. See:

Family Sharing  https://support.apple.com/en-us/HT201060

Set up Family Sharing https://support.apple.com/en-us/HT201088

First wipe the iPhone: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Then during setup you can create a new Apple ID for her: Set up your iPhone, iPad, or iPod touch - Apple Support

Under Step 6, tap on "Forgot Password or don't have an Apple ID", and follow the steps to create a new one.

Alternatively you can create a new prior to setting up the phone, and then sign in with it when asked.

I suggest you use the steps in the article below before giving the phone to your aunt. That will make it 'her' phone and help prevent potential future problems.

Selling/Giving Away Device.