You need a washing ball, cardboard, glue and fabric.
Cut a circle from the cardboard the size of the top of the washing ball and glue a strip of cardboard to its edge. Make a hole in the middle of the cardboard.
Put padding on top and then glue the fabric.
Cover the wash ball with the same cloth.
With a thread, pull the fabric of the center of the cover inwards and glue on it a "button" which is taken from a piece of paper with a piece of fabric glued to it.