Accidentally changed username in netplwiz – now I can't open anything

I wanted to change the name "Client" to something else, so I followed a guide that said to use netplwiz. But I accidentally changed the wrong field and now I can't open anything on my laptop. Even trying to check system info gives an error: "The parameter is incorrect." I tried adding a new user through cmd but got access denied.

Laptop is an MSI Cyborg 15 running Windows 11. Anyone know how to undo this without wiping everything?