You’ll need cotton fabric i like to use quilting material, elastic, a sewing machine.
First, cut your fabric 40 inches long and 4” wide. You can make a fuller scrunchy the wider you make the fabric or a thinner one the less wide you go.
Measure your elastic about 12 inches or smaller depending on how tight you want your scrunchy to be.
First, turn the raw edges of the ends in and sew in place.
With right sides of the fabric together, sew the long side. Turn right side out.
With a safety pin, connected to the elastic thread it thru the tube of fabric making sure one end stays outside the outer edge and the other end makes it out the other side.
Pin together to hold in place and sew the two ends of elastic together.
Now sew the open edges closed with a top seam.

Don’t forget to trim the elastic!
And there you have a flashback scrunchy for an updated look!