Difficult... – Sketchbook® Review

So I really like this app, but where’s the undo button?? I’ve looked for it countless times, always unable to find what exactly I’m looking for. I’ve used the erase button, but I can’t erase without ruining the photo I inserted behind the drawing. Please answer my few questions or fix these errors and I will make sure to change my rating? thanks!!
Review by KateMay07 on Sketchbook®.