Events typically get into Notist when someone creates a presentation. If you are an event organiser you can also create your event in Notist, however you may discover that someone has already created your event and want to update the details.
If you can provide us with a way of confirming that you own this event in some way then we will be happy to give you the right to edit it. You'll need a profile for us to assign it to, so make sure you're logged in and have a username. Then raise a support ticket with a link to the event in question and a way for us to confirm you, and we'll sort it out.