You're close. Attached is a JetCat manual.

You need to decide whether to use the Aux Channel, most of us don't and typically use single channel mode.

Look that up and do as you want. I do the following for failsafe & throttle range:

Set Low Throttle end point to -150% and bind. Reset Low Throttle end point to -100% & High Throttle to +100% and bind again.

Do a Learn RC. On the GSU, hold Select Menu & power on. Hold the button until it says release to Learn RC.

Set trim low & throttle low and press the Select Menu button.
Set trim high & throttle low and press the Select Menu button
Set trim high & throttle high and press the Select menu button