1. Upload the video to YouTube

Youtube video listing

2. Edit the video and click the “Subtitles” menu item

You should see that there are automated captions already in place, click the "Duplicate and edit".

Subtitles menu item

Duplicate automated captions

Edit the text of a caption

Timing will not be set until the text is complete.

YouTube captioning keyboard shortcuts

Publish the video when complete

YouTubve unpublish captions button