Heatmors have tongues like most other pokemon, and can be used as such. However, our tongues also have the ability to safely ignite due to our anatomy.
Fire types have a specific gland organ that produces various gases or liquids that can combust through the addition of a spark. Heatmors produce nearly pure oxygen (thanks to the third nostril which is our tails). Unlike other fire types, this gland is connected to a section of our lungs. Also, our tongues produce Biodiesel, which has a flash point (the temperature that a liquid can be combusted with an igniter) of 130 °C/266 °F. Heatmors have a natural temperature of 93 °C/200 °F, so our tongues aren’t burning all the time. Anyhow, we Heatmors can cause ignition within our gas glands by causing sparks to form from rubbing our natural Pokemon energy against the gland. With this ignition, the fire can travel into our lungs from the gland, which then travel to our mouths and tongues. During this time, our energy is also heating up the inside the our mouths so that the biodiesel will reach its flash point. Once the fire reaches our mouths, our tongues also ignite! Thanks to our developed glands, Heatmors can control where the biodiesel is produced in order to change where the fire is kept. Also, our lungs are split into two sections, so that one part can be combusted while the other can keep taking in oxygen and spreading it throughout our blood vessels. These two tactics allow Heatmors the ability to produce fire for an indefinite amount of time.
This was a long explanation, but I like to help others know exactly how something works.
P.S. Our tongues bulge inside of our mouths, allowing more space and length for our tongues.
Against All Odds inspiration and reference, for Logan.