Well, the short version (sorry it's late here) is to click in the black space (where instrument name normally is) underneath the volume slider in the mixer window.

This will pop up a menu, and from that menu you go to "Select MIDI Patch", you should have a submenu and you should see 8 or 10 default patches (these can be set as your favorite patches somewhere in BIAB) you will also see menu item "Select General MIDI Patch".

Picking the "Select General MIDI Patch" menu item will bring up a list of the 128 GM patches, that are used in the internal DLS Synth. You can change your instrument patch here.

As I said this is the short version, because there is a place in BIAB to set favorite instruments, and also to set which MIDI channel goes to which track in BIAB.

Also there is a setting in BIAB somewhere to save program changes, when your song is saved, that way you won't have to re-select the instruments next time you open the song.

The manual is a good place to start as far as setting up default MIDI channel per Track settings, favorite patches, and also the "save patches with song" settings.
But if you need more info. I can try to get a couple of screen shots tomorrow.

Hopefully this helps.

- Jay

MacPro 5,1/12 core@3.46GHz -- OS X 10.15.7 -- ATI 7970 -- 32 Gig RAM -- Crucial 500GB OS SSD -- Samsung EVO 1TB Audio/Sample SSD -- BIAB 2024 -- Logic Pro X -- Cubase Elements 14 -- Too many plugins