Video Tutorial

Chain 12
Make rows with half double crochet to have 3 cm less then the width of the head
Taking the front and the back loops (one of each), on the next 4 rows
Join with slip stitches the 1st and the last row

With the colour of the detail, make 3 double crochet on each free loop (front or back). Don’t cut the yarn at the end of each row, continue on the following rows to finish with the free loops makind the waves

See the tutorial for more information