If you really just changed the ownership of the
sudo command--that is, the file
/usr/bin/sudo--then you can fix this by using
pkexec instead of
sudo to run
chown and change the ownership back. This command does that:
pkexec chown root: /usr/bin/sudo
pkexec will prompt you for your password (as would
sudo if you were able to run it).
root: means the same thing as
root:root, in case you had changed the group owner as well.
If you have changed the ownership of many more files besides
/usr/bin/sudo, and in particular if you have changed the ownership of all files in
/usr/bin (which would also happen if you changed permissions on
/usr but passed the
-R flag to
chown, specifying recursive operation), then that will not be sufficient. But based on the description you have given in the question--that you have specifically changed the ownership of
/usr/bin/sudo--running that one
pkexec command should be sufficient.