Be aware that switching to using an entirely different AppleID account without first removing the Activation Lock will cause the issue that you describe.
In order to recover use of the iPad, you must recover access to the AppleID that was previously used to successfully activate the iPad. Assuming that this AppleID was yours, this shouldn’t be difficult. If instead the AppleID belonged to somebody else, you must independently secure their cooperation in removing the Activation Lock - as otherwise the iPad is and will remain useless to you. You can find the procedures here:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
An AppleID account is intended to be used for life. If you need to change the primary email address that identifies your account, or your secondary (recovery) email addresses or trusted telephone numbers, you simply need to update your AppleID account as necessary.
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
Change, add, or remove Apple ID payment methods - Apple Support
Few of us will have the luxury of forever keeping the same email addresses or telephone numbers - sometimes these needing to be changed for a variety of reasons. However, updating our AppleID account, maintaining access to our data and purchases, is easy and relatively straightforward - accommodating life’s many changes as they occur.
If you do wish to change and use an entirely different AppleID, first ensure that you have disabled the Activation Lock that will otherwise cause difficulties in the future. You can disable the Activation Lock by disabling the Find My iPad service from iPad settings before trying to use a different AppleID account:
Settings > [Your Name / AppleID] > Find My > Find My iPad - set to OFF
Having disabled the Activation lock, you can now sign-out from your old AppleID:
Settings > [Your Name / AppleID] > Sign Out
Presumably you’ll want to keep any iCloud data that is locally stored on your iPad. If so, accept the opportunity to keep a local copy of your data (e.g., Calendar, Contacts, Notes, Keychain Passwords etc.) - as otherwise this data will be wiped from your iPad as you sign-out from iCloud. After signing out, a restart of your iPad is recommended:
Restart your iPad - Apple Support
After restarting, you can sign-in to your new AppleID account from iPad settings. Any iCloud data that you saved to your iPad during the previous sign-out will be merged with your new AppleID account.