I guess this is the app you’re referring to? This is the only exact match for “Wanikani” on iOS, no app matches on Android.
This is the community thread of this app, but there hasn’t been much activity recently: New iOS app
I don’t own iOS devices so I can’t say for sure, but it seems that the community is using Tsurukame these days, you should maybe look into it: [iOS] Tsurukame - native app with offline lessons and reviews