I'm not with Laminar Research, just a fellow simmer in the UK.
When you start a new flight with any aircraft installed with a Garmin FMS, the flight management system, in this case the Garmin G1000, will remember the operational flight plan (OFP) that was programmed into it during the previous flight.
To delete the previous flight plan from the G1000, please do the following:-
1. Click once on the Multi-Function Display (MFD) to make it larger and easier to read
2. Press the Flight Plan (FPL) button located on the right hand lower side of the MFD, just above the FMS rotary switch. This will open the Active Flight Plan window as per the following photo:-
3. Press the MENU button also located on the right hand lower side of the MFD, just above the FMS rotary switch. This will open the Page Menu window as per the photo below
4. Activate cursor (press centre of FMS rotary switch) and scroll down to Delete Flight Plan and then press the ENT button to clear the previous flight plan
5. Enter or import new flight plan as required
Hope this helps :-)