My iPhone's asking me someone’s else's Apple ID and password to confirm

To confirm what?

If you mean to sign into the phone, Read this article about removing Activation Lock --> How to remove Activation Lock - Apple Support Unless you have the account information that set the lock, the original receipt from Apple or an Apple approved vendor, or can demonstrate legal inheritance from a deceased owner, you cannot remove the lock; return or recycle the device.

If you mean to update an app, delete the app and download it with your own account.