Those are not keys. You are in the transposing instrument menu, which offers C, Bb, Eb, F and G, the five instrument settings.

 

Set the transposing instrument back to C. On iPhone, iPad and Android, tap the chord chart settings button at the top of song view (Aa on iPhone and iPad, A on Android), tap Transposing instrument and choose C. On Mac, open Preferences and choose C under General. On Windows, open Settings and choose C under General.

 

Now change the key from the player controls. Tap or click the key, then choose a new one from the twelve on offer.

 

For the full guide, see Transpose a song on the iReal Pro website.