Eyedropper will only show up if you haven't made a stroke before.
You have to draw the actual shape (lines, curves, circles, rectangles, triangles...) and not lift the pencil after you're done, it will snap into the refined version of your shape.
You can resize it by dragging the pencil(still don't lift it). You can also touch with a second finger of your other hand (while still not lifting the pencil) to get the "perfect" version of that shape. And also you can touch and drag with a second finger to move the shape around. Once you lifted the pencil you can't manipulate the shape anymore (at least in the current version of the app).
And if you go to preferences > gestures > Long press delay, you can adjust the time it takes to activate the eyedropper/ autoshape (0=disabled)
Hope this helps