Maybe this will help. here are some screen shots of the program mix on my 9C.
Yours may be slightly different if its a newer model. My switch E for example is only a 2 position switch.
This is the first screen you see in the advanced programing mode. I selected mix 1
This is the first screen you see whan you first open that mix. Its where you set the amount of OFFSET by adjusting the RATE amount anywhere from -100 to zero to +100
From that screen, you scroll UP with the cursor buttons to get to the main screen below where you enter the following:
MIX = on or inhibit. You want it on. It may also display OFF if the switch is in the wrong position. You dont want it to say INH because that means the mix is inhibited or disabled.
MAS = master channel. You want to set it to OFFSET - mine says OFST
SLV is the slave channel. You set that to the chanel that goes to the auto pilot
LINK - try OFF to start but you may need it ON.
SW: is the switch you want to use
POSI: is the position of the switch. When you move round selector button, this value will change from UP to UP/CENTER or center or center/down or down or NULL. Select the position you want to program for this mix. NULL = no switch is active. Note that when the switch is in the position you have selected here the mix will show as ON.
When you scroll down one more time you are back to the RATE screen above. Again use the round button to select an offset amount.