Select Unshaky as the editor in the Gallery of your choice.
You will get a screen like this.
Use two finger zoom to zoom in. Tip: zoom in to a place where you can easily measure the direction and extent of the motion.
Drag (with one finger) the arrow in the direction of the blur, dragging it to the extent of the blur.
Tip 1: You need not hold the arrow! You can just about drag anywhere on the image and it will move the arrow head.
Tip 2: If you see bright or dark "ghost"s you can reduce them a little using the "Dark" and "Bright" dials.