It's not often you need to wind a ball of yarn into a skein since you usually go the other way around, but this trick is helpful when recycling yarn.
How to Hand-Wind a Skein of Yarn
My 3 Methods for Winding Yarn – Elizabeth Smith Knits
How to Hand-Wind Yarn Into a Ball, Hank, or Skein
How to wind a skein of yarn into a ball (with no equipment)
Learn to Wind Yarn Without a Winder • Banana Moon Studio
What Is the Difference Between a Hank, a Ball, and a Skein?
How To Wind a Ball of Hand Dyed Yarn From a Hank. - New Garden Farm
What is a skein of yarn & the differences between hanks and balls.
What is a skein? Demystifying names for yarn bundles. - Shiny
Knitting Tutorial: How to Wind a Skein of Yarn into a Center Pull
How to Wind a Ball of Yarn Into a Skein or Hank
How to Hand-Wind Yarn Into a Ball, Hank, or Skein
How to Unwind a Hank of Yarn
A Field Guide for Yarn – Part 1 - Tink & The Frog