Hi,
I use MIDI Macros on an iPhone and Lightning Camera Connection Kit, which I find brilliant! It lets you set up 'buttons' for program changes (and any other MIDI message). I don't know whether it works over Bluetooth, but is great over USB to the Rev2. The developer also makes an app to enter program changes manually or increment/decrement, but the buttons of MIDI Macros work best for my needs. In fact I didn't gig the Rev2 until I found this app, so I would thoroughly recommend it.
https://audioapps.nl/app/MIDIMacrosIt works on my iPhone 8, but not an old (original) SE for some unknown reason.
If you try it let us know what you think.
Andy B