La Danse's Pointe Shoe Video Series number 3: Sewing Ribbons and Elastics.
This is a long video so if you're looking to skip to a specific part of the guide, click on the timestamps below:

Equipment 0:00
Cutting the ribbons 2:40
Sewing the ribbons 4:15
Elastics 9:08

If you are complete beginner to sewing, full explanation of the technical terms are covered in this Essential skills guide
   • Essential Skills for Sewing Pointe Shoes