There are several places where you might see a different Apple ID. Yours would most likely be #3 below.:
1. In Mail if you want to use a different, or more than one, iCloud account. Settings -> mail -> accounts -> add account -> iCloud
2. Messages and Facetime. Sign into a different Apple ID for these services in Settings. Note this has to be the same ID for both. Go to Settings > Messages > Send & Receive, and make sure both your telephone number and Apple ID are input there and both show a checkmark. If you need more help, check this link: Add or remove your phone number in Messages or FaceTime - Apple Support .
3. In the support article: If you subscribe to Apple One and use a different Apple ID for iCloud - Apple Support Apple alludes to using a different Apple ID just for media, subscriptions, and purchases, but doesn't describe how to do this. See if these work:
In iOS/iPadOS: Go to Settings > [your Apple ID] > Media & Purchases. Sign out of the current ID and sign in with a different one.
In Ventura or later: First, quit Settings. Then, in App Store, choose “Sign Out” in the Store menu, then click on the “sign in” button that appears in the main window. You can then sign into the other account. (from: Using different Apple ID for media & … - Apple Community )
4. Use a different Apple ID to share purchases with Family Sharing as outlined in Use a different Apple ID to share purchases with Family Sharing - Apple Support
Note that if these were downloaded using his ID, you will have to delete the item and redownload it with your ID. If you used Family sharing the same applies since you are no longer in the same family group.