You have to link your Neopets account to the respective mobile app before you can complete a mobile specific quest.
First, you would need to link your Neopets account to a NeoPass. (for more info, refer to this article )
After migrating to NeoPass, you will be able to link to Faerie Fragments and Tales of Dacardia.
Once the mobile linkage is achieved, the mobile specific quests would be unlocked for you.