I've been using a Keyboard and Mouse on my Pocket edition for months now and just recently I was facing issues running minecraft on my mobile, after couple of reinatlling its fine now.
But unfortunately it reset my keyboard controls.

As I'm trying to change my controls back to how I usually have them, I can't seem to change the Sneak/crouch/fly down button to anything else apart from default 'Shift' key or 'CTRL' key.
I used to have the 'F' key as my crouch now it won't change to anything other than those two. Also, I can't move (Use WASD keys) or open inventory or anything without having to constantly have the Ctrl key on hold all the time.