The English text is “For any starting direction of gear bit A, make it point left if the blue ball is released or right if the red ball is released”.
So there are four possible setups to test:
A starts pointing left, blue ball released
A starts pointing left, red ball released
A starts pointing right, blue ball released
A starts pointing right, red ball released
And A should end up pointing left, right, left, and right respectively.
Or, if you want to streamline the testing have 2 blue and 2 red balls loaded, start with A pointing left, and release the balls one at a time in order blue, red, red, blue, which should leave A pointing left, right, right, left after the individual balls, allowing you to test each combination without touching anything except the release levers.
And, yes, it’s a pretty straightforward puzzle if you can see (or guess) the key idea, but it also makes sure you have a key concept that can be used in future.