You will need to install a user script manager extension to install this script.
This script can load a geometry file and overlay it in the Waze Map Editor. Simply go to the Areas tab on the left, and scroll down to the new controls that have been added.
The data format is detected automatically using the file extension, and the following formats are supported: GeoJSON, GML, WKT, KML, and GPX.
If you need help getting your geometry files to load, please contact the author.