Paste in your entire HMD config, or just the "tracking_to_eye_transform" section, or select a base config from one of the more popular configs for GearVR lenses:
After adjusting the sliders, press button to generate output below. NOTE: when putting back the generated config onto the HMD, you may have to deal with removing curly braces before after, and adding, removing commas to make it JSON compliant. Go here to check if your reassembled config is valid JSON before trying to upload it to your HMD jsonprettyprint.com. The final config should look something like this when it's complete:
In general, the "0" config is most middle circle of the lens, and "2" is the edges.. 1 is somewhere in between. It's a very simple relationship, but still there's more too it than that! In addition, usually you'll adjust 0 by the most, then 1, then 2 in order of most to least. You probably don't need to adjust by ANY MORE than about .02 in any direction. Usually you'll want to always go positive additions, but sometimes a bit negative may help. Try to tweak and see if you can improve your distortion settings.