big sur, cannot remove previous administartor
I bought an open box iMac retina 5K, 27-in, 2020 and trying to use migration assistant but it asked for admin authorization from pev owner. I tried to remove using terminal but wouldn't work. I did a clean install of big sur and did a restore from time machine managed to get my stuff from old comp (high sierra) onto this one but once again asked for previous admin password ti migrate data. I could tell it was previous because it was misspelled. when go to users & groups in sys pref only I am listed there are no other users. my folders are on the desktop but are all empty
iMac 27″, macOS 11.6