Welcome back to the Wefugees Community and thank you for sharing your question!
Lawyers in that field are normally described as "Fachanwalt für Ausländerrecht" or "Anwalt für Asylrecht/Migrationsrecht" or something similar.
However, I want to recommend you to contact either a migration counselling office in your area (their services are confidential and free of charge) or the refugee council of your state (i.e. Flüchtlingsrat Berlin, Flüchtlingsrat Niedersachsen, Flüchtlingsrat NRW...) first.
I am sure, that they can recommend you a lawyer or even support you with your issue directly.
I hope this helps and please feel free to get back to us with any further questions.
All the best,