3 position switch on devo 10

Im looking to set up the three position switch on my devo 10 as my flight mode switch, it is linked to apm 2.6 on a 450 quad, the receiver is spektrum AR6100, the reason being is i need three flight modes for my CAA course and i only have one spare channel, after a few days of playing with the TX i cannot figure out how to set this up, it was really simple with my spektrum TX but that died
any help would be greatly appreciated.

Well, without knowing how it was set up on the Spektrum Tx, or what the model expects to see, it's sort of hard to tell you how to set up deviation for it. Impossible to do it and know it's right.

You need to configure APM to pick flight mode based on your one spar channel (you've got a 12 channel Tx here - how many are you using!?!). Then set that channel up on the Tx to have values of -100,0,100 based on the switch position. You can't do that in the Standard GUI - you have to use the advanced one. The easy way is to set the channel to a complex mix type, and use three mixers. Each one has a curve type of fixed, switch set to the appropriate FMODE (0, 1 or 2), and the scale value set to the value you want output for that switch position.

apologies for the late reply, Im at sea with limited internet at the moment, the ar6100 receiver was only bound and set up in the APM 2.6 flight controller, this is for a 450 quad , on the spektrum tx i had to use mixing of two switches to create up to four outputs but i wanted to use the one switch/PWM channel for flight mode as i also wanted a spare channel for retractable landing gear for better photography, I understand that i have to use a complex mix to do this and the three values of -100,0 and 100 as i can see these in the monitor option but have absolutely no idea how to do it, i did try but as i remember i was struggling to get my head around the three F-Mode switches onto the one PWM channel.
Hope this makes sense to somebody