If you want all files with a certain extension (not the 1 specific file) to be opened by a certain app, do the following:

1. Right click the file and click `Get Info` (or highlight file and hit <kbd>cmd ⌘</kbd> + <kbd>i</kbd> )
2. Change `Open with:` to preferred app
3. Click `Change All...`
4. Click `Continue` in the confirmation box

![Get info screen][1]
![Confirmation box][2]


  [1]: https://i.sstatic.net/e17ji.png
  [2]: https://i.sstatic.net/y1SIp.png

Is this what you meant to do? This is different from right clicking a file and choosing the 'Always open with' option. That seems to only apply to the specific file, not all files globally.