First of all, you should carefully decide the keyboard system to be
learned. This depends on the music you want to play and the
sheet music you will use.
The decision also depends on the instrument you have got. Basically you may use any layout as long as its tonal range is sufficient. Be aware that the fingering is different among the systems and, perhaps some chords are easier to play on one system compared with an other. However, if you are member of an ensemble with other bandoneons, it would be a huge advantage to have a common system.
After that you start learning the 4 keyboards, which is for most of us, very time demanding. It is not a surprise that students try to find ways to shorten the process. In this place contributions from people giving their experience are presented: keyboard layout, chord tables, learning tools, and also a game!
But at the same time you need some success. Besides some technical
training you should start playing easy pieces with a narrow tonal range.
Beginners' exercises for piano are a good alternative if you don't have
You can learn fairly fast using only one hand.
Learn all the notes for both bellow senses and by separate.
The coordination of both hands simultaneously is far more difficult.
While you progress learning the keys you can choose exercises with more notes.
Later play simple but real pieces to learn the handling of the bellow.
The bellow is not an air pump and has a prominent importance in getting
the real sound.
All the first exercises should be played as legato.
To learn this you may play a scale holding every note as long as you
can but with constant intensity. Imagine you are playing a cello.
Always check if your are completely relaxed!