Only you have any comprehension as to what, how and where you attempted to make a change to your AppleID credentials. Perhaps you need revisit the process to understand where something may have gone awry:
Change your Apple ID - Apple Support
Change your Apple ID password – Apple Support
What to do after you change your Apple ID or password - Apple Support
If you need to resolve an issue with your AppleID or password, they can be recovered here:
https://iforgot.apple.com
To recover your credentials, you’ll need access to one of the following:
- Your primary email address mailbox that corresponds with your AppleID
- Any of the secondary/recovery email addresses that should be configured for your AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID
Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.
More information about recovery of your AppleID:
If you forgot your Apple ID - Apple Support
More information about recovery of your AppleID password:
If you forgot your Apple ID password - Apple Support
When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:
https://appleid.apple.com
I hope that something here proves to be helpful with troubleshooting and resolving the problem.