If your group has not got an account, you can learn to set one up here.
You'll need to get this signed by the Community and Societies Manager, so complete the form electronically, and email it to email@example.com
If your group has one/might have one, but no one on the current Exec knows the details, you can contact ISS to retrieve them.
(You must be a registered exec/committee member on lusu.co.uk before ISS can grant you access or setup your account. Find out how to do this here)