RoboHelp has the possibility to integrate third-party tools for Grammar-/Spell-Check.
The integration will take place with an API-Key and an Endpoint site.
I guess you’ll need to ask the RoboHelp support about this. The fact that there’s no username indicates that this was not made to support LanguageTool. Isn’t RoboHelp a web-based software so that you could use the LanguageTool browser add-on?