Very simple and very fast!
It also can be used as Hair Clip.
Measure your wrist and add 5 cm (2 inches) to your wrist measurement = your bracelet length.
Measure the diameter of your brooch and add 0.5-1 cm (0.2-0.4 inches) = your bracelet width.
Draw a rectangle on the felt, using your length and width. Cut.
Pin a brooch in the center of rectangle. My brooch has small holes, so I also sewed it to the felt in several places.