1st, decide if you trust this person enough. Using script tags may lead to the permissions compromising and vulnerable.

2nd, go to the “Network Admin -> Settings -> User Role Editor -> Multisite” tab and turn ON the Enable "unfiltered_html" capability option.

3rd, go to the site where you user has ‘administrator’ role and open ‘Users->User Role Editor’, select ‘administrator’ role, turn ON the ‘unfiltered_html’ capability. It’s located at the ‘Deprecated’ group.