First, just try this. When it asks for a password, don't type anything. Just hit enter. Sometimes it's a ghost and there really isn't any password used.
If that doesn't work, then there really is a password. The only way I know of doing it is to use BIOS to change it. I'd normally not tell anyone to do this, but it's the only way I know of how on a computer that's locked down. Try following these directions:
https://www.techwalla.com/articles/how-to-change-the-administrator-password-in-biosWhen you start it back up, you need to have a finger already on that F2 key and immediately press it and hold until you see a different screen from normal. Also, BIOS is a nice blue place, but it's not the blue screen of death.
For Dells, if F2 doesn't work, then try any of these combinations until you get one to take you there:
DELL
On a newer Dell computer, try the F2 key while you see the Dell logo.
Alternatively, try F1, Delete, F12, or even F3.
Older models might use CTRL+ALT+ENTER or Delete or Fn+ESC or Fn+F1.
My favorite way to get into one is ctrl+alt+Delete because it usually works on any I've ever touched no matter how new they were.