macOS: Setting up an administrative account from a user account without admin password
Apple has a guide that covers all the permutations and combinations (iCloud / FileVault / forgetfulness / no password at all)


https://support.apple.com/en-us/HT202860


If you have FileVault turned on, you likely need to reset the password with Recovery boot.


Reset admin password without the old password


If you don't have FileVault turned on, you can simply make a new admin account and then use that user/password to make any other non-admin accounts back into admin accounts.


How can I get admin access to a Mac without knowing the current password?


The above covers my favorite way - remove .AppleSetupDone and make a new account, but some people prefer to not worry about a new admin user and just do the full reset with ddcl

You can no longer just force the reset from the OS that's running - that's the same as defeating the reason to have a password and Apple has patched all the easy / known ways to do that I believe.