Windows 10 lost administrator rights and cant insert administrator password to change settings

I have changed my username from netplwiz.

I have restarted the pc and now I am a guest account.

I go to change settings but I can't insert the admin password!

I have only option to insert a smart card and I cannot enter a password!

How can I resolve this issue?

Answer

I solved by inserting a disk installation of Windows 10 I could run the System Restore and go back to the time before you change the username thank you all for the interesting replies that might be useful in the future.

Many thanks
Massimo :)