i can help you with this being a lowly space cadet.....
Get in the shower with it on, sounds silly i know (it works) Once soaked (the band keeps itself dry enough) simply mould to your desired shape. I.E. the RAF way.... and then stand under shower again. Once this has been completed for a little while take the beret off. Fold to allow the shaping to be bent across the fold and pin under something heavy, or with bulldog clips. Allow to dry...well near enough dry and then repeat and after the 2nd time it will be shaped perfectly!!!