Hi,
The standard procedure is all Apple says about this:
1. Go to https://appleid.apple.com and sign in.
2. In the Sign-In and Security section, choose Apple ID.
3. Enter the email address that you want to use as your Apple ID.
4. Choose Change Apple ID.
5. If you changed your Apple ID to a third-party email address, check your email for a verification code, then enter the code. Learn what to do if you didn't get the email. --> If you didn't receive your verification or reset email - Apple Support
6. If you use services like iCloud or Messages to share with friends and colleagues, sign in to those services with your updated Apple ID. --> What to do after you change your Apple ID or password - Apple Support
For more details, and how to do this if you have a mobile number ID, see the document Change your Apple ID - Change your Apple ID - Apple Support
That makes me wonder if you have restrictions set on the account: If an app or feature on your device is not working, it may have been disabled using Screen Time, or by an IT administrator if you are using a device owned by an employer or educational institution. See how to use Screen Time on an iPhone, iPad, or iPod touch by clicking here --> Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support
Related information about how to use parental controls on your child's iPhone, iPad, and iPod touch to restrict access to features --> Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
