Depending upon what app you are working in, there may be an undo feature in the app. In Pages, there is an Undo button in the upper left corner of the screen wheel the document is open for editing.
The IOS keyboard has an undo key on it. Tap the ?123 key on the left side, and the UNDO key appears. If you then tap the #+= key, undo becomes REDO.
You can also shake the iPad to bring up "Undo Typing" on the screen.
I use a screen protector on my iDevices, but I still and always have used a slightly damp microfiber cloth to clean the creek and a dry microfiber cloth to dry it off. If you are an old Mac user - you may still have a couple of the black cleaning cloths that you used to get when you bought a Mac or a MacBook. I use those.
You can get microfiber cleaning cloths at a lot of the electronics stores if you don't have any lying around.