Engineer,

In order to answer your question thoroughly, folks would need to know which version of BIAB you have.

If you have the "full version" UltraPAK or higher, you will have the most options. (and if you have the 2019 version of that, you will have the most current options)

In my opinion, your best option for what you want is using the MIDI Supertracks.
Simply enter your chords into BIAB, then select a MIDI Supertrack into one of the tracks. (Solo that track). Generate a track and export the MIDI that is created. Simple as that.

You can "audition" any of the the MIDI Supertracks in the selection screen by double-clicking the choices.

A number of the piano RealTracks also have associated MIDI files that can be export (though I believe the MIDI Supertracks are a better choice). I don't use this option, so others who have used it might discuss this...

If you have any questions regarding any of those steps, simply ask...

If you have an example that you can point to - a YouTube video perhaps - of a similar sounding song, you might get some suggestions for folks here about what piano tracks to try...

fj