Hi,
To reschedule a call, meeting or other created event in Gmail, you have to click on the
Calendar icon on the right side, to show the calendar and scheduled events:
Click on the scheduled call, to show the details. You can modify an event by clicking on the pencil icon on the top:
Click on the date or time to modifiy it. Then click on
Save to apply the changes:
Alternatively, you can make the same changes from your calendar: