How to make less salty Fermented Black Bean Stir Fry
There are two ways to reduce the saltiness of the finished dish: reduce the amount of salt you put in (in this case difficult, as it is in the sauce, so you'd have to put in less sauce) or increase the amount of water that stays in the finished dish. For the second option I personally have the following strategies which may or may not suit your taste:


add more veggies or tofu or other watery ingredients without salt
add yoghurt or any other fresh topping that contains no salt
also make sure that the tofu you add is not too salty, if possible add plain tofu


or as mentioned in the comment to your question you could make your own sauce, one good recipe I found was here: http://www.daringgourmet.com/how-to-make-homemade-black-bean-sauce-or-black-bean-paste/ It tells you how to transform fermented black (soy!) beans into a sauce and also has some interesting examples how you can use it and it doesn't seem very complicated to do.

Of course if you are adventurous you could also try fermenting soy beans yourself, but that's another story.