If you're on Windows, download the harmony_2019XXXX.zip file, unzip it, then change to the harmony_2019XXXX directory and double click on "harmony_2019XXXX.exe" (XXXX is for the date and time of the build, which I can't remember right now...).
If you're on Linux or Mac, you'll need to download the harmony_source_latest.zip, unzip. Then download Dr. Racket Scheme for your platform from https://racket-lang.org/. Then start Dr. Racket, the File -> Load "harmony.rkt" and "Run" (button on the right top of the IDE window).
Hope that helps! Thanks very much for taking a look!