The conversation kit needs/should be installed by a professional and is available at time of purchase. I utilize propane and requested the conversion at time of purchase.
When my dryer was delivered and installed I watched as they did the conversion to propane on site. They had to take the entire dryer apart to change the natural gas jet to a propane jet.
It is like changing the jets in a carburetor for a car.
So, I highly recommend contacting a professional or having Best Buy do it during an installation.