Not arming with arduflyer apm 2.6

I am not able to arm Quadcopter through FS-i6 transmitter all thing done well by mission planner then also it’s not arming please resolve this proble…pls arming proble come when I try to active three mode switch from youtube it’s all done wrong then I reset transmitter and again bin it, and also calibrate, all motors working on receiver but not through a apm…pls can any one help and resolve my problem