Before resetting I would ask the question "why did the heater fail". If it was because you forgot to open any air vents then, yes go ahead and do the reset, by pushing the red reset button on the actual heater unit behind the rear bulkhead.
However if you were getting heat out of a vent and then suddenly you started to get cold air, the unit has a fault and should be looked at by maintenance. The ignitor has probably died and I can guarantee you that no amount of button pushing is going to get it going again. However if a heater was working and then popped the button I would consider whether I wanted to reset it very carefully
The reset button is popped by the overheat sensor. This sensor is designed to stop an over temp condition and the possibility of an in flight cabin fire.
Mindlessly resetting it without troubleshooting the problem is not IMO the best idea......