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I have looked on the manual for your thermostat and hold means that the temperature will "hold" at what it is set at. Did you change the batteries because the unit was not working?
You can view the manual at the following link.
No, there is now way to reset that thermostat. There is also no way to get rid of the problem you are having. I have seen it go back to normal after a week or two but have also seen it never go back to normal. You should probably replace it.