I agree that “Bubble” is confusing. Perhaps they meant “Part” of the song.
The BBMO MIDI Editor is everything within the red box (item 27)
To best answer your question, if the 4 bars you want to remove are at the end of the song, you can probably do that using the BBMO however, if those 4 bars are in the middle of the song part (OPB_FINAL), you are much better off using a digital audio workstation (DAW) such as Reaper (Mac and PC) or Logic Pro X (Mac). I’m basing this based on how Support answered another user’s question in this link: Adding new Bars in BBMO
Daniel or Brenna will weigh in to my reply if there’s a better way.