You can boot into recovery mode and then look at /etc/passwd to find out the username of the user you added. It will probably be user 1000. Then you should be able to use 'passwd $username', where $username is the name of the user that was created, to change the password.
You can boot into recovery mode and then look at /etc/passwd to find out the username of the user you added. It will probably be user 1000. Then you should be able to use 'passwd $username', where $username is the name of the user that was created, to change the password.