I changed the battries in thermostat. I hear my furnace running but the fan does not come on to blow heat. Is there a reset button I need to push to fix ? If so please explain how.

Try moving the lever on the thermostat from auto to ON at the thermostat for the blower. The blower should come on if not then you will need to track down the problem with the furnace. Now if the blower comes on when you move the switch then the problem is with the blower circuit in the furnace.

When you have a NO brand name along with a NO model number furnace it is very difficult to tell what the problem could be.