It doesn’t appear to be a popup. Here’s the pattern, but by doing this you are missing a graphic that might be helpful. Here is the link also.
Beginner basic straight skirt
Skill level: Beginner
Gauge: 16 stitches and 25 rows / 4 inches Can’t get the right gauge?
Yarn: Four 3 oz. skeins worsted weight yarn
Elastic: About 31 inches of 5/8 inch firm elastic length may vary
Extra: Two 60 inch lengths of contrasting sewing thread
Skirt bottom: With waste yarn, cast on 87 stitches and knit 4 rows. Set counter to 0. Change to main yarn and knit 120 rows.
Shaping: Using 2 pronged or 3 pronged transfer tool, decrease one stitch on each side on row 120, 124, 128, 132, 136, 140, 143, 146, and 149. (Making “fully fashioned” decreases will make the sides easier to hem.) 69 stitches.
Waistband: Knit one row with both main yarn and contrasting thread held together. This will make it easier to pick up these stitches later. Counter = 150. Knit 12 row even. Counter = 162.
Forming waistband: Hang claw weights about 4 rows down from top of work on right side of work along the entire row. This will make it easier to rehang lower stitches. Push stitches on needles behind latches. Pick up stitches from row 150 (where contrasting thread is) and hang in the latches directly above. This takes some time and concentration! Pull stitches in latches through stitches behind latches. Bind off with latch tool method.
Ribbing: Rehang 87 stitches from waste yarn. Knit 10 rows with same keyplate. Release every other stitch 10 rows and latch up. Bind off with back stitch.
Finishing Sew side seams except leave one side open at the waistband on the inside but do not break yarn. Insert elastic through waistband being careful not to twist (a large safety pin fastened onto one end works well). Overlap ends of elastic 1/2 inch and sew together securely or butt ends of elastic together, wrap with a scrap of fabric, and zigzag ends together securely. Tuck elastic inside. Close seam in waistband. Remove contrasting thread if visible. Optional: With contrasting yarn, stitch an X on the inside on the waistband at the center of the panel that you want to be the back.