Do_set_Relay from Joystick?

Hi all ,

I am using Arduplane 3.4 with radio FRsky tranise , send control channel using telemetry by active the joystick options ,

as shown in the pic below I set all of my channel ( roll , pitch , yaw , throttle , mode )

but now I want to use the command " Do_Set _relay "

I couldn’t use it as Channel , and I find it in the buttons option , but don’t know how to assign it to any switch in the radio ?

Is it possible to do that using the Frsky RC ? and how ?

I hope some one can help .