Assign 2 channels to a 3 position switch

On my Flysky Fs-I6S transmitter, with a flysky 10 channel receiver, I would like to use a 3 position switch to control to separate channels as follows

  • low position - do nothing
  • Middle position - control channel 7 - set to high
  • High position - control channel 8 - set to high

Can this be done and if so how would I need to setup my transmitter.

Thank you