My memory is shaky as it's been a while since I used it, but I vaguely remember there being a hidden built-in administrator account that could possibly be used

My memory is shaky as it's been a while since I used it, but I vaguely remember there being a hidden built-in administrator account that could possibly be used in this situation. Can't remember if you would need to set a password on it / enable it ahead of time though Edit: this might be what you meant by the admin one (rather than a)