Hi Andreas
I'm not gonna be much help, but here is an older discussion about that machine:
Need an owners manual for a Dial 'n Sew Mdl 516 or similar
Maybe one of them found a manual and can help
Also, Victorian Sweatshop is a good resource - this forum is all about vintage machines and vintage enthusiasts (not all old people)
- maybe someone there can help?
https://www.victoriansweatshop.com/
welcome!