Welcome to the Wefugees Community and thank you for reaching out to us.
First of all, I am unfortunately not an expert on family law. But I made some research and read, that applying for the "determination of the paternity" at your local family court/district court (Familiengericht/Amtsgericht) might be a possibility. You could also ask for a "Beratungshilfeschein" at the district court, if you can prove, that you can not afford to hire a lawyer. Holding that paper, you can consult a on family law specialized lawyer for a small fee (currently around 15 euros). Nevertheless, the lawyer can not support/defend you in the actual legal proceedings in court.
I hope this helps and please get back to us with any further questions.
All the best,