Cowls (and hats) are tricky to block because they are knitted in the round. If you lay them on a flat surface, there will be a folding line which is not very nice…
Fill the inside with something, for example with towels. I just finished my daughter’s cowl, here is a picture about the blocking:
I hope you found this tip useful! If you have a good trick or if you can’t find a solution for a knitting problem, please share with me! Hopefully I can help with it.