In order to access backend of an event, the administrative has to sent you an invitation via GEVME.
As a recipient, this is what you will see on your end.
The Invitation will be sent via email, hence, do check your inbox to check if you received as such:
Click on the 'Accept the invitation and start collaborating' button.
Once clicked, you will be directed to the page where you should login to your GEVME account and 'Accept Invitation'.
Once you have done those, you should be able to see the event and access backend based on your assigned User Role.