Stuck, updated to sequoia but now don't have admin access and can't turn off updates, or enter recovery, please help!

Hi, I'm completely new to OCLP, I bought a preloaded usb from eBay with instructions so I could download MS word and one drive for uni work, and this is as far as I've got-

Ive been able to boot sequoia from my hard drive, except every time I power on, I have to select the drive before it will let me log in. I somehow managed to transfer sequoia to my hard drive even though it was asking me for admin details to change the drive. I checked settings and my account is labelled standard, not admin and there's no admin account. I got this Mac from my sis in law and her details don't work either..

I was able to do the post install root patch but I can't get into recovery to change admin, so I can turn off the updates, nor can I change any settings e.g. screen timeout, which I was able to do before I did the update.

I'm afraid of an update being forced and ruining the Mac, I'm relying on it for uni work currently :(

Any help would be appreciated!