I moved your question to here, the iOS forum.
Audiobus has a long list of apps that work in the Effects section:
http://audiob.us/apps/
You should be able to find a pitch shifter there, perhaps a guitar (pedal) app would be the first place to look. Keep in mind that the complete audio track goes into the effects section from iReal Pro, so all the sounds you hear will pitch shift (meaning the cymbals etc.) so if you think there are just some notes or an instrument is not in pitch, then this will not work. Otherwise if you are using an audio app for recording, you could possibly mute and just record (with the pitch change) the instrument you want to correct (assuming it is the complete instrument sound you want to change).

Are you sure some of the instruments or notes are out-of-tune? If you can be more specific, we can check it is within our tolerances.