Thank you for your question!
I answered how to prepare for an appeal interview before on the following thread, please have a look:
Questions regarding my Appeal interview
And this thread can help as well, even if it's related to the BAMF interview:
How can I prepare for the hearing at the Federal Office for Migration and Refugees?
Hopefully this can give you some guidance, but I urge other members to share some experiences with you here, too :-)
All the best,