I gave my iPad to my grandchild.

follow the guide

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

1. Log into Apple's Data and Privacy website with your Apple ID. You may be required to perform two-factor authentication to continue. 
2. Under the heading Delete your account, click the link to Request to delete your account.
3. On the new page, select a reason for deletion from the dropdown box, then click Continue. 
4. After going through a checklist of things to bear in mind when deleting the account, click Continue. 
5. Review the Deletion Terms & Conditions, tick the checkbox, and click Continue. 
6. Tell Apple how to receive status updates on the account's deletion, then click Continue. This can include a different Apple ID, an email address, or a phone number. 
7. Make a record of the access code Apple provides, and click Continue. 
8. Enter the access code to confirm what you noted down was correct, and click Continue. 
9. Check the final reminders of the effects of account deletion, then click Delete account. 
10. On the confirmation screen, click Sign out.

This has been derived from https://appleinsider.com/articles/21/01/04/how-to-delete-an-apple-id-account.