sudoers file corrupted

You can edit the file from first link.

https://askubuntu.com/questions/73864/how-to-modify-an-invalid-etc-sudoers-file

If it fails, try the options, (mostly first one) as in below link.

https://askubuntu.com/questions/799669/etc-sudoers-file-corrupted-and-i-cant-run-pkexec-visudo-over-ssh