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There may be a reset but I need the model number to tell you where it is. But it sounds like you had a power surge when the power came back on and it fried the thermostat. A reset won't help that. You're probably going to need a new thermostat.
You first should remove the leads from the R & C terminals and the batteries for at least 2 minutes. Be careful to not let the leads touch. Then replace the leads and batteries
You can also try, press the up & down arrows and the FAN button simultaneously. Thermostat will go blank momentarily then return to normal display after displaying all segments simultaneously.
If that doesn't work you probably need a new thermostat.
There really isn't much more I can add. I've covered all the possibilities. I'm logging off for the night. If you have more questions I'll respond in the morning. If you don't have more questions I'd appreciate a favorable rating.