You can amend or cancel your flight plan after it has been filed with either the CANCEL or AMEND buttons in ForeFlight Mobile on the Flights page, by calling the 1-800-WXBRIEF phone number.
VFR plans can be amended (if not activated) or activated until 2 hours after your ETD. Once a VFR flight plan is filed, it can be amended (unless activated) or closed at any time using ForeFlight Mobile.
IFR flight plans can be amended or canceled until 30 minutes before the ETD, at which point the plan is transmitted to ATC.
Filed plans are automatically canceled by ATC if not opened/activated within 2 hours following the departure time.
All ICAO and FAA/Domestic flight plans are filed with Leidos.