Arbitration board

If your journey is of a private nature, then, in the case of flight disputes, you have the right to contact the ‘Schlichtungsstelle für den öffentlichen Personenverkehr e.V.’ (SÖP), Germany’s independent arbitration board for public passenger transport that oversees all carriers.

You may do so if you have concerns relating to

denied boarding, long delays, or the cancellation of flights;
the destruction, damage, loss, or delayed transportation of baggage, or
breaches of duty in the transportation of disabled passengers or passengers with reduced mobility, or
breaches of duty in the conclusion of carriage contracts,

provided that

you have already contacted Discover Airlines about your concerns and have not received a reply within two months or
you are dissatisfied with the way your concern has been handled or disagree with how your claim has been processed by Discover Airlines.
your concern is not already pending before a court or at one point was pending before a court or has been settled.
your trip is a private trip.

To "Schlichtungsstelle für den öffentlichen Personennahverkehr e.V. (SÖP)"

To conciliation request

The postal address is:
söp_Schlichtungsstelle für den öffentlichen Personenverkehr e.V.
Fasanenstraße 81
10623 Berlin

The European Commission also provides a platform for Online Dispute Resolution (ODR):

To platform for Online Dispute Resolution (ODR)