To remove the two factor authentication for webmin, edit the file /etc/webmin/miniserv.users.
On this line:
Remove the word totp from the line that begins with your username.

The lockout on login can be removed by running the following on the server:

service webmin restart

Refresh the page after restarting the service.
After logging in, under Webmin>Webmin>Webmin configuration>Two factor authentication>Authentication provider: None