Welcome to the board! I do love a challenge and went looking for you. Do you have any idea how old the machine is? There seems to be a connection between Kenmore sewing machines in the 1950's and Gritzner. I also found a great info page on Gritzners in German (my German is rusty but it translated for me).
https://www.naehmaschinenverzeichnis...inen/gritzner/
But alas ... no mention of a manual anywhere that I could find. There are some pics of a VZ machine showing the cams inserted if that helps you. Good luck!