You can erase in Imagink with these two methods:
Using a real eraser and the Ring
Put a Ring onto a physical pen-type eraser. Select the Eraser tool from the Imagink app and erase directly on your paper. The marks are erased on both your paper and the digital version of your drawing.
Using the Eraser tool
Select the Eraser tool from the Imagink app and erase unwanted marks by tactile input on your iPad screen. You can adjust the eraser’s parameters (diameter, blurring) as you wish.