"However, you are keen on inserting line breaks in the places of your choice into subtitle blocks, here's the tip:
1. Transcribe and sync your video from beginning to end - once you've inserted line breaks, you will not be able to edit your subtitles without losing the breaks.
2. Download the subtitles as a file in SRT format.
3. Edit your file in a text editor of your choice, inserting line breaks where you need them (and yes, it's an awesome idea to keep a backup copy of the original SRT file, just in case something goes wrong).
4. When you are done, upload the resulting file back to your video at www.universalsubtitles.org (or use this file elsewhere as you like)."