It's impossible to have cutters or moulds in all sizes. Let me show you a simple way of making a starfish freehand.

This is a part of the Seahorse Tutorial, that is why the size of the starfish is defined and the templates start from 31.

3.

Place the star template (33) on the dome. Hold it gently.

Make small round cutouts with the piping nozzle as shown in the photo.