See in the Piano Roll view it's set to the Bass track
and the View/Edit is set to Program
once you remove any instrument changes you just set it in the Mixer/Track to the instrument you want.
See as I move up/down to select the instrument to change to, it will set it to that instrument when the cursor passes otherwise it will use the default you set it to in the Mixer/Track menu.

FULL SCREEN then to zoom in to see what's happening use your ctrl+ mouse wheel

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ReaTrak Biab & Plugin in Reaper
Free Biab Chord Picker Tool