Hi PoodleCanoodle,
Welcome to Apple Support Communities. We understand that you're having an issue with accessing some Settings on your iPhone. We'd like to help.
From what you've described, it sounds like you either have Screen Time enabled on your device or your device is managed by another person or school/company. Is it possible that you iPhone is managed by your work, employer, or parent? If so, you will need to ask them to change the Settings to allow you to adjust your information on your iPhone.
However, if you have set up Screen Time on your own device, you may be able to make those changes your self. Check out how to use Screen Time here:
Turn on Screen Time
1. Go to Settings > Screen Time.
2. Tap Turn On Screen Time, then tap it again.
3. Select This is My [device] or This is My Child's [device].
After you turn on Screen Time, you'll see a report showing how you use your device, apps, and websites. If it's your child's device, you can set up Screen Time and create settings on their device or you can use Family Sharing to configure your child’s device from your device. After you set up your child’s device, you can also use Family Sharing to see reports and adjust settings from your device.
With Screen Time, you can also create a dedicated passcode to secure settings, so only you can extend time or make changes. Make sure to choose a passcode that's different from the passcode that you use to unlock your device. To change or turn off the passcode on your child's device, go to Settings > Screen Time and tap your child's name. Then tap Change Screen Time Passcode or Turn Off Screen Time Passcode, and authenticate the change with Face ID, Touch ID, or your device passcode.
While in the Screen Time Setting, you can look through it to see if some of your Content & Privacy Settings are enabled so that you cannot change your Account information.
Check that out and let us know if that works.
Cheers!