Since ergogen generates Kicad v5 files, you must design the footprint in v5. Otherwise you might use functions, such as certain arcs, that are not supported in v5 and the resulting PCB won’t open.
For a good guide on how to create footprints in Kicad, check out:
An Intro to KiCad – Part 4: Create a Footprint | DigiKey
The Kicad v5 module comes with a large collection of footprints in the kicad/modules folder.
Add those libraties to your global libraries list:
You can then use these as a starting point and copy them into your footprint.
You can also find existing footprints for many components on these websites:
The websites might say “Download EasyEDA footprint”, but many (or maybe even all) models come with kicad files.
You might also be interested in some keyboard specific libraries: