For any upcoming event, if you want to change the details like its date, location, the maximum number of volunteers, etc. you can do this easily by editing the event. You can edit all the details of an event that you entered while creating the event.
Please note that to edit an event you should have one of the following privileges:
Creator of the event
Co-ordinator of the event
Admin rights on the platform
The video below shows you just how to do that.