Someone else’s Apple ID on my phone

Hello DblTrbl618,

Thank you for reaching out in Apple Support Communities. To ensure that your granddaughter's Apple ID is removed entirely on an iPhone, you'll want to follow these steps:

1. If you paired an Apple Watch with your iPhone, unpair your Apple Watch.

2. Back up your device.

3. If you purchased an AppleCare plan for your device, cancel your AppleCare plan.

4. Sign out of iCloud and the iTunes & App Store. 

∙ If you're using iOS 10.3 or later, tap Settings > [your name]. Scroll down and tap Sign Out. Enter your Apple ID password and tap Turn Off.

∙ If you're using iOS 10.2 or earlier, tap Settings > iCloud > Sign Out. Tap Sign Out again, then tap Delete from My [device] and enter your Apple ID password. Then go to Settings > iTunes & App Store > Apple ID > Sign Out.

5. If you're switching to a non-Apple phone, deregister iMessage.

6. If in-store trade-in is available in your country or region and you're trading in at an Apple Store, stop here, do not erase your device, and visit your nearest Apple Store to pick up your new device. After a Specialist completes your trade-in, they'll work through the remaining steps with you in-store. If you're completing your trade-in online, continue to step 7.

7. Go back to Settings and tap General > Transfer or Reset [device] > Erase All Content and Settings. If you turned on Find My [device], you might need to enter your Apple ID and password. If your device uses eSIM, choose the option to erase your device and the eSIM profile when asked.

8. If asked for your device passcode or Restrictions passcode, enter it. Then tap Erase [device].

9. Contact your carrier for help transferring service to a new owner. If you aren't using a SIM card with your device, you can contact them to get help transferring service to the new owner.

10. Remove your old device from your list of trusted devices.

This will ensure that your granddaughter's Apple ID and associated data is removed from your iPhone. These steps are outlined here for you to reference: What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Kind regards.