Thread yarn onto yarn needle, thread through stitches and pull tight. Pull yarn through to the wrong side.
Make a pompom, the simplest way is to use your fingers. You can use the same Bernat yarn used for the brim of the hat, or different white yarn if the chenille is too tricky to work with.
Attach pompom to top of hat by pulling its ties through to the wrong side and tying them together with the red yarn already pulled through.
Weave in ends and block/shape if desired.