Find the event in Slack
Everyone in the Slack workspace can add and edit events! To do so, first find the event you'd like to change. The easiest way to do that is type "/events" in the channel to see all the events posted. When you find the event, click "Show me details"
Click "Edit"
Next, you'll want to click the "Edit" button. This will bring up the window to modify any/all details about the event.
Once complete, click "Update". This will change the event details going forward.
Note: Editing an event will post a notification about your changes, in every channel that event has been shared to.