I'm not a fan of editing text on an ipad, so I do most everything on the computer.
I usually grab a chord version of the song from Ultimate Guitar. Then I'll copy and paste them into a ChordPro converter (I use http://ukegeeks.com/tools/). Before I run the formatter I will fix the mistakes and align the chords. Run the formatter, copy and paste them into a document.
If I have to make a quick fix in ST3, that bracket button to the left of the midi and play buttons is super helpful.