How to reduce the heat on a gas burner
1. Simmer/Burner Plate

You can use a simmer plate or something to diffuse the heat. For example:


http://www.thekitchn.com/good-tool-burner-plate-for-low-107122
Google: Heat Diffuser


From the first link, a suggestion is to use a cast iron skillet as a heat diffuser. That should work in a pinch.

2. Adjust the Flame

Alternatively, some stoves allow you to adjust the flame level. I'm not a technician, so please do this at your own risk, read the manual, etc....