Is there instructions on how to make messy bun hat?

Assuming you have some knitting knowledge, here are some good tutorials using both the loom knitter and traditional methods:

http://happyhourprojects.com/messy-bun-hat-pattern/

https://www.studioknitsf.com/knit-messy-bun-hat/

If you mean a hat to fit over Messy Bun. Why not Knit - Sew or Crochet a Straight piece of work that will fit around your head and deep enough to reach up to your Bun. Sew into a tube and then make a cord and thread it through the work at the top and draw up - Tie in a Bow - Knot both ends.

This could always be lengthened and turned up and or Add to top by adding Lace etc. and embellished with flowers or what ever you like.......

If your meaning to knit or crochet, go on the site: Revelry.com for lots of free patterns.

https://www.youtube.com/watch?v=81aax9M0cA8

Tons of patterns on Pinterest!