First, go to your Computer.
Next, go to the app titled "BabaZone"
Then, scroll down until you find the flamethrower option.
After that, Purchase the flamethrower. OR if you don't have enough credits, get some by doing commissions.
Lastly, wait until the top right of your screen says "A package arrived", head over to the package area, press the button below the 1 on the monitor, and pick up the flamethrower.

Hope this guide helped!