Originally Posted by Nell2ThaIzzay
I would imagine that Singer's "fixing" comment is in regards to Xavier, Magneto, and possibly Rogue.
There's no actor even cast as Cyclops in the film, so I doubt they undo that. Unless Marsden and Famke have been secretly cast, I wouldn't expect much undoing outside of Xavier, Magneto, and Rogue.
Technically Ratner already did the fixing with those characters. From what I've read about the Xavier scene at least it seemed like Ratner's attempt to save Xavier from that fate since he didn't seem to have the choice not to have Dark Phoenix vapourise him.
As for Rogue and Magneto. The cure was already shown not to have worked properly. Talking to my brother, who is a very casual viewer in my opinion, he was by no means surprised at seeing Magneto again and very quickly brought up the X3 scene with Magneto displaying some power at the end.
Aside from that. Singer by no means spells out what will be fixed. It really could be anything at this point. As far as Cyclops goes that is just part of my own speculation (though there is unconfirmed rumours of Marsden traveling with Halle Berry).