You may not like my answer, but there really is only one way!
Don't run before you can walk. That means learn each hand separately before you place the hands together. Why? 1. You learn faster. 2. you don't fight fingering mistakes which you will develop a TON of bad habits if you do 2 before 1 hand at a time.
You have about a 14 week head start on me, but let me say that there are only 2 "secrets" to the entire process...
Let's use a simple scale as a good starting point, start with the basic C-major scale.
1. practice separately, start SLOW and build to a good speed.
2. start SLOWER, 2 hands togehter, and again build to a good speed..
In expanded format here is I am doing it:
1. practice each hand separately until you can do each side to about 100 BPM (beats per minute), speeds on a metronome for 5 minutes on each hand non-stop without errors (google for online metronomes, which are fine ). Start with 1 octave up and down. START SLOW, Perhaps 30 beats per minute with eighth notes (2 notes per beat). For the Conservatory exam, the minimum speed is 80bpm for grade 1 exams. By the time you can do 100bpm with each hand separately, you are ready for an easy transition to step #2.
2. go back to even SLOWER, like 20 BPM. Do left and right hands together for *1* note, (ie only C),... repeat each note 5 times, the do 2 notes (C, D), repeat 5 times. then 3 notes (C, D, E), then 4... and so on... concentrate on proper fingering on both sides at ALL times. STOP if you make an error and start over. Once you can do the complete octave 2 times with both hands with no errors at 20 BPM, add 5 beats to the metronome, and then 5 more... and then 5 more. STOP increasing speeds if you make mistakes, slow down 5 beats and practice until you can do 2 runs without error. Continue to about 50 BPM. Once you can do several repeats of one octave without errors at 50BPM, slow down to 30BPM, and do 2 octave runs. Same process, if you can repeat 2 runs of 2 octaves smoothly and without error, add 5 BPM to the metronome.
After 5 days of this (30-45 min a day), you develop not only hand coordination, but you will find that the process starts over slowly once you start a scale from a different row as the left hand pattern changes (there are only 3 basic variations of all major/minor/etc... scales... 1st row, 2nd row, 3rd row!).
Concentrate while practicing, and you get a nice surprise... the 2nd scale (let's say a G-major scale), it takes you a mere 4 days to get to the same level it took you to get to the C-scale's 5 days. Why? You've developed coordination!
The basics are the things that take the longest... this process takes WAY longer if you did not develop slowly. Example, I can play 2 songs on Free Bass now easier than I can play the 3 scales and triads on hands separately for the exam, that is because I am just starting my path, and though I am 61 years old it takes me longer to get a strong base. One has to build a strong base to build your "house of music" on, because if you build on quicksand (take short cuts and don't focus), you will need to rebuild and correct for those errors later on. I stopped playing the songs for a month, to build on my base.
There is a reason they say that it takes about 10,000 hours of practice to get good at any instrument, and Free Bass accordion is no different. My big advantage is that I am confident with my right hand, so I double up on the left hand to try to eventually bring it a lot closer in matching capability. I can do a C-scale at 225bpm all day long, but that is physically impossible to do even on the left hand alone... for now.
BTW, if I may ask, where in Ontario are you located, Phillipe?
