Administrator name and password

Easy. You have messed up your account folder name and user name.

So first of all you have to check if your user folder name is the same as in this setting: Change the name of your macOS user account and home folder

but if you are unable to make any changes you must contact apple support.

What you need to do is to create a new Admin user and change the permissions for the current one, this cannot be done without support, so they could see that every step is correct.

Contact Apple Support

Restarting Setup Assistant to create Admistrator this is what you need, but it is not that easy because terminal commands are involved

Are there no users with "Admin" below their names?

The reason for asking is that changing your account from Standard to Admin would require logging in under an Admin account, unless you have an older Mac in which case another solution is possible.

What macOS version are you using? To determine that, read Find out which macOS your Mac is using - Apple Support. Tell me what it says next to Version.

Open  (Apple menu) > System Preferences... > Users & Groups to see a list of users.

If you are the only user of that Mac, then you are its Administrator. Your User Name will appear under Current User, and below, it should say Admin.

That is probably not what you are seeing, so describe what's different.