Change the privileges of my event to allow or disallow guests to make changes

Allow guests to modify a calendar entry

It can be easier to negotiate a meeting time or collaborate on the event description when your guests also have access to edit your event's details. For example, if you're planning an event with multiple people it could be helpful to have one person add in the agenda in the description, while another invites the guests and confirms the event location.

While this is possible by sharing your entire calendar, some situations call for granting access to specific events or you may not be interested in giving sharing access to all of your calendar entries.

For this purpose, Google Calendar provides the option to allow guests to modify events to which they're invited. This means they can change the event time, location, or description, or add additional guests.  

To enable this feature in an existing event, follow these steps:

1. Click on the event, then click Edit event details.
2. In the event details page, you'll see a list of options in grey boxes on the left side.  Look at the Guests can portion of the Guests section.
3. Select the modify event option in the Guests can section of the event details.
   
4. Click Save. Now your guests can make changes to the event details, including the name, description, location,

While creating a new event, follow the instructions above, clicking to the Event details page when creating an event from the calendar view (if you create an event using the Create Event link, you will automatically see the Event details page)

Reference Allow guests to modify a calendar entry