basically you figure out which one is closer to where it should be, and then track the other blade.

How you do that is unplug the motors and put the heli in normal mode at 0 throttle. The pitch should be right around 0, for some heli's it's slightly negative. The other way is to put the heli in idle up and 50% throttle and trim should be at 0 pitch. Whichever blade is closer, go with that one.