In theory it's simple but in reality it seldom is. If it is replaced with an identical servo it should have the same rotation direction. EXACTLY where the servo centers is usually a little off but for most applications it's a minor trim change as long as you get the servo horn on in the right place.

After you take the old out and put the new in turn on yuor radioand helo and put the horn on where it will be the closest to get the swash level. use sub trims from there to get it as good as you can see it. This is assuming you are using the same servo as the bad one. Most of the small helos the end points isn't really used as they are not that pickey.


Double check directions though or it'll be a wild first flight.