Unfortunately I can't change the simbrief type- the flightplan has correctly "B737" in the flight-plan.
The message is telling you the airplane type in MSFS is 737, while the type in your Simbrief flightplan is set to "BBJ1".
While BBJ1 is a way to colloquially indicate the Business variant of the 737-700, the official ICAO type designator for it IS still B737, as indicated in the official ICAO database so, both PMDG and GSX have it correct as "B737".
If you want to continue to make flightplans on Simbrief and use the BBJ1 naming, maybe because you have a ready-made profile for it, you can edit the ICAO type in the GSX airplane configuration editor, and set it to BBJ1