On this website, WPMU Dev is installed for 10 days.

On this website, WPMU Dev is installed for 10 days. I cannot make any changes. I have received this email :

Howdy XX
Welcome to the community !
You will need to turn off mod_security by adding this to your .htaccess file
https://gist.github.com/tech55541/54028dbdd956127e3c12

I did it but it still does not save the changes.
What to do. I need help before I lose patience with it