There’s no way to directly connect Fat Shark goggles to a DJI drone, as the systems use completely different connection protocols.
There is a workaround, but it requires buying additional gear like DJI Goggles or the DJI Smart Controller, Raspberry Pi, and using CosmoStreamer. So not really worth it. ( too expensive and complicated )
I’d recommend getting a DJI Goggles that’s compatible with the Spark, or going for the newer DJI Avata 2, or even better, FPV drones.