I find that ..as an example of using 2 ndbs/adf
put the inner marker into adf1 (the left one of the 2 on the radio panel) and the outer marker into adf3 (right one on the radio panel) and then use the OM/IM selector switch on the 2d panel to switch between which one is active.

The OM/IM switch is near the landing gear lever and is a left/right switch with a green light beside it when IM is selected

or so methinks