First, remove the top. Deburr the can's upper edge. Elevate the can in the sleeve to the desired height. Lock it in place with a pushpin, preferably two at opposite sides.
Make 16 vertical cuts around in the can's upper rim that are equally spaced around the can's circumference. Use the slots as a visual guide for placing your cuts. Drag the tip of your scissors against the sleeve's upper rim as you cut so that they all terminate at the same level on the can. Then fold the 16 flaps down and manually press them against the inner rim. Roll the slider around the rim to flatten the flaps in a circular shape around the lip of can.