Hello @Edmon
Welcome to the Wefugees community.
While we wait for someone to share their own experience with their asylum application in the transit area of an airport, here is another thread that might be of interest for you:
https://www.wefugees.de/102233/international-transit-frankfurt-airport-asylum-application
Also check out this link with extensive information about the procedure:
http://www.asylumineurope.org/reports/country/germany/asylum-procedure/procedures/border-procedure-border-and-transit-zones
Best regards,
Thorgen