The answer is simple, but doing it can be difficult. Your challenge is to balance the temperature in the freezer with the temperatures in the fresh food compartment. Most of your units will have one cold plate in the freezer and distribute the air in two other compartments with air dampers. Like a sound system the cold control is the gain main control and volume is the amount of the air you control with the damper in the fresh food compartments.
You must have the air temperature in the freezer 0 to -3 * and 36 to 38* degrees most all thermostat’s are in the refrigerator and cooling is in the freezer you must set the control the gain in the refrigerator to get the ice cream hard and the damper halfway open the get 36* in the refrigerator with no ice crystals in your milk. You move the control to mid-way 4 or 5 and damper set about c or d move the control up one number at a time not to open the damper to fare open. Let the unit run 24 hours then check the ice cream and milk adjust again once you get the right temperature it will stay set. Maintenance cleaning of condenser coil once a year will keep your unit running well.