Multisite Admin Account has been deleted – need to retrieve

I have installed Multisite and it has been working successfully for the last number of weeks for up to 15 of my students who are creating student projects. Howevever, one of the students has managed to delete the superadmin account. Whenever I try to login at sitename/wp-login.php I get the following message :
This user has elected to delete their account and the content is no longer available.

I cannot even bring up the login screen to enable me to login to the Network Admin dashboard to try to resolve the problem.