I wrote a free pattern for a scrunchie knitted either with 2mm, 3mm or 4mm double pointed needles and some yarn leftovers. You can find the pattern on ravelry (link in comments)
KnitPurl Scrunchie Knitting pattern by Anab Naiyer | LoveCrafts
How to Knit a Scrunchie | an Annie's Creative Studio Full-Length Episode - YouTube
Scrunchie Knitting Pattern, Quick and Inexpensive Gift