I don't really know everything that is in an ice machine, but assuming there is a compressor motor in there somewhere, the short answer is that you cannot change it to 50hz.
If the motor is designed for 60hz operation, it will run at 5/6 of normal speed at 50hz. This will reduce the work done by the compressor. This is true for any fans as well as anything else motor-driven.
It would be much better to get a product designed to run from the appropriate power source.