Chrono Download Manager can do this, I could not find a way. But, I did have … show moresuccess downloading the remaining part of a video using a popular (free) command line tool called ffmpeg:
To get to the standard Chrome download manager (Ctrl J) you need to first go to … show morethe Chrono settings (gear icon) and under General uncheck the "Override browser's downloads page and enable Ctrl+J keyboard shortcut". Then you can get to the standard Chrome downloads manager click the three dots next to the partially downloaded item you want and select Resume.