OK, Repetier has this firmware tool online, but how to use it for the Vertex?
Sorry I don’t understand what you are asking.
If you are trying to change / upgrade the firmware use these instructions.
http://manuals.velleman.eu/article.php?id=31
Use Arduino software 1.0.6 or below.
You can download it from this link.
https://www.arduino.cc/en/Main/OldSoftwareReleases#previous
That is the Marlin firmware.
I would like to use the Repetier firmware.