Concepts saves the data for every stroke and selection you make, instead of just the last stroke like most apps. We call it an Unlimited Undo. We also have a Redo if the undo was the mistake, instead.
If you want to Undo or Redo something, try these ways:
Way #1: The Button
If you look at the tool wheel or bar, you’ll see that two of the slots aren’t for tools at all, but have curving arrows in them. The upper arrow faces backwards and un-does anything you don’t want to exist, while the lower one faces forwards and re-does anything you undo. To use them, tap as many times as necessary.
When the tool wheel is docked in the corner, for example on the iPhone, you might not be able to see these buttons. The wheel spins when docked, so swipe through the options and you’ll find them.
Way #2: The Gesture
Sometimes, using the buttons might be too much work. By default, Undo is set to a two-finger tap on the screen, and Redo is set to a three-finger tap. (You can change these in Settings -> Gestures at any time, find the gear icon on the top status bar.)
Way #3: The Stylus
If your stylus is equipped with a shortcut button, you can set the button to Undo in Settings -> Stylus. Connect your stylus, then set the shortcut.