Go to releases for the current build. Download concat.exe if you are on windows and concat if want to use it on ubuntu.
You need ffmpeg for this tool to work. On windows you can get it here. Make sure that ffmpeg is in the same directory as concat.exe. On Ubuntu "sudo apt-get install ffmpeg" will work.
VODID is the number you find in the url of the vod eg (https://www.twitch.tv/videos/123456789 => 123456789), the first HH MM SS is the start time and the second HH MM SS is the end time with HH = hours, MM = minutes, SS = seconds.
Call concat.exe VODID HH MM SS HH MM SS
Call ./concat VODID HH MM SS HH MM SS
Blog post about the tool.
Send me feedback contact@concat.org