I assume you have the RCin connected to the RFD900X pin4 GPIO1_EXT already.
You load the Yaapu telemetry script on the X9D, and follow this for some improvements to your 900X/TXMOD setup:
To get Yaapu working on the X9D you might have to pull out the SDcard to load all the files onto it, the X9D doesnt seem to play as nice doing all that over USB.