Changing and saving scenes is not a feature yet implemented in the iPad app for the X32. This request is on a long list of improvements to come for the iPad app. I have copied some comments below that Mr Behringer made about this subject recently.
"I have been using the latest beta of the upcoming Version 2 XiControl iPad app for the X32 and thought I’d share it with you on this forum.
Since we released Version 1 some weeks ago, many of you have asked about added functionality including effects processing and other control from the iPad app. While we are not ready to release V2 just yet and it will take some more months, the following screen shot will give you some idea of where we’re going with XiControl.
We're also currently developing a very cool iPhone Personal Monitor Mix app. As mentioned earlier, this is just the beginning of a series of revolutionary products surrounding the X32 and all other consoles to follow.
Of course this is all pre-release and completely against the advice of our software team so keep it between us; I wouldn’t want to get in trouble.