There is no direct option to edit the captions in Captionizer.
You need to do that on the YouTube page.
You can edit the original caption from YouTube (before reading it in Captionizer) by going to https://studio.youtube.com and then editing your video.
Click on More Options and there you will be able to modify the existing captions.
The same goes for editing the translated captions.
Click on Subtitles button from the More Options page of your video (On YouTube) and there you will see a list of all translated captions.
Edit the captions that you want and save them