1) Copy User Control to your UserControls folder (example: C:\Program Files (x86)\GeneXus\GeneXus15\UserControls for Genexus 15)
2) run "genexus.exe /install" on command line (Genexus will not open) - C:\Program Files (x86)\GeneXus\GeneXus15\Genexus.exe is the default path for Genexus 15
3) Open Genexus as usually...