My renter messed up the thermostat, help!!!

Got a call from a tenant that his thermostat was reading EH, so I tried to help him get it back on cool, but no luck. We tried everything, probably pushed too many buttons, etc. I even looked online at a manual to see how to operate it and set it to cool, but it was of no help. Right now the unit is turned off and the windows are open. How can we get it set to cool again. Burning up in Florida! Thanks.