1. 

   Click on Assign to me & Start button. A new tab will open on Matesub.

2. 

   Signup for a Matesub free account and start reviewing the subtitles!

3. 

   Correct all subtitles and confirm them with the appropriate button.

4. 

   Once finished, close Matesub and mark the review as completed.

You can follow a video tutorial explaining the whole process here.