The retract servo is on Channel 5, switch E. Power up the transmitter and receiver.
1. Press and hold "Mode/Page" key.
2. Rotate "Press" button to highlight "E. Point".
3. Press and hold "Press" button.
4. Press lower "Select/Cursor" button repeatedly until the triangle symbol is beneath number 5.
5. With "Switch E" in the down position turn the "Press" butonn clockwise or counterclockwise to adjust the servo arm until the mechanical limits of the linkage is where desired. Notice the left "percent" symbol will change.
6. With "Switch E" in the up position turn the "Press" button as above to adjust servo for opposite linkage movement.

Adjust the end points so the servo doesn't hum or chatter and no binding exists in the mechanical linkages.

When you're done press the "End" button repeatedly to return to the main screen.

All of this presumes your retract servo is connected to Channel 5/Switch E.

Good luck.