Yes, you have to activate the governor in the TX to use the Direct Set by TX Mixing under the basic setup in the CGY750. This is how you accurately set the headspeed in the 750 using the TX instead of a 3-position switch. This is the best way as you can adjust the heaspeed from the TX. Do not set the CGY750 to Using By 3-Position Switch!
The endpoints (Limits Setting) are used in the CGY750 to set both lowest and highest throttle (carb) based on your linkage. Your TX should have ATV/Endpoints of around
±100 to avoid binding if your servo to carb linkage is properly set up. Mine TX ATVs are -99, +97.
I use a switch (SA) to toggle between gov on/off as well. This helped with tuning the engine originally and to set my TX throttle curves (fall back in case governor fails). I may take the switch out of the gov activation process now since my heli is tuned and the curves are spot on, closely matching the gov.
You will likely just use the stick (No Switch, Gov Basic Step 6 in manual) for gov activation. The thottle stick position determines when the gov is activated (say 30% throttle). Remember your throttle curves for ID1 and ID2 will (should) always be above this set point.
That's really all there is to the basics of setting up the gov in the CGY750. Fine tuning can be done in the Advanced menu, but I did not find this to be needed except I reduced the miniumum throttle from 40 to 30.