How do you know that the air mix servo is moving to far in either direction? Does it make noise, hit something? Do you get cold air when selecting hot?
If it moves too far, it's most likely due to the linkage as the stops are built into the linkage. The only other possibility is a bad servo, or your ecu is messed up and sending voltage for too long (though highly unlikely)
As far as I know, there is no reset calibration procedure for any of the ac/heater servos. They're controlled by the ecu and either operate smoothly, as intended, when voltage is applied, or you have to replace it. They're not serviceable.
attached pic is the test procedure for the air mix servo:
