This can be achieved in two ways:
1) You can create a flow to update Outlook Calendar event based on the Event Id, Subject , start and end time matched criteria. This can be triggered if something gets modified in the Sharepoint list. You can apply a condition on the flow, which checks if the Status is not equal to "Submitted", and if this returns true, you can perform an action to update calendar event, else stop the flow.
2) You can directly trigger the flow from the PowerApp's submit button to save the Edit form details. You can apply a condition in the app itself to check the mode of current form, please use below expression:
If(Form1.Mode <> New, trigger flow, do something)
Through this, you are checking if it is a new form then do something, if not then trigger the flow to update Calendar Event.
You can just pass the EventId, Subject, Start time and End time and the calendar will be updated.
Hope this Helps!
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