A static torque check usually requires some weights of known mass -- like barbell plates. However, in your case, since the discrepancy is so large, you might not need laboratory accuracy; you could probably just use your body weight. Balance first on the left pedal and then on the right, and check the torque reading to see if they're close. [Edited to add:] Since the discrepancy is so large, just put your bike parallel to a wall with the front wheel wedged into a corner with cranks horizontal. Then put your head unit in torque mode and stand on the left pedal, with maybe the backs of your fingernails of your left hand against the wall to support you. You don't want the weight to be supported by your hands, which is why you're using the backs of your fingernails on the wall; they're just for balance. Then do the same thing for the right pedal. The whole thing should take about 2 minutes.

If you can't do that, then you have to do a dynamic test. Ride up a steep hill first at slow slow speed; then at fast speed. Then go to one of the online power websites, like analyticcycling.com, and see whether the power for your speeds is about right. If the hill is steep enough, you don't have to worry about aerodynamic drag.