No offense to anyone here who might be, but hvac isn't rocket science.
The tools needed consist of a pipe wrench and pipe dope.
Buy a fitting or two, some pipe and DIY. Make sure the pipe is secured, away from other conduits and electrical lines. If your still unsure of your work just have a qualified tech inspect it after.
I ran the gas line for both of my fireplaces in my remodel. Just depends on where and how you have to run it?
Is the garage connected to the house or detach?
Where is the closest point of connection? My water heater was close so I split off of that line.
If you pay attention and take your time it is pretty straight forward. Add a t connection into the existing line. Make sure everything is sealed up.
Flex hose although a bit more costly can be your friend in many places.