My operating system is Windows 10. If more information is necessary, please ask.

I did a fair amount of research both with Google and even more dismayingly with the search underneath the title bar for this question. Unfortunately, one "solution" crushed my hopes when one possibility (software) gave me a prompt that it only runs on Windows 7 and Vista. I tried compatibility mode and it still didn't run!

I wanted to read a `.dat` file and accidentally set the file association with sublime text!

When attempting to revert to defaults within Settings it only reset the default apps for the Internet, video and other stuff. 

There's no "x" for the option further down in the "choose default apps by file type" menu. I can't remove it within Windows. I'm still hunting, but I'm worried that an update or use of a `.dat` file might blue screen me due to my mistake.

The more hunting I did, the more I realized that not fixing this could brick my machine.