This edge starts with a foundation round of (SC, Chain 2, Skip 1 stitch) repeated, with (SC, Chain 2, SC) in the corners.
Step 1: Skip 1 Chain loop, Treble Crochet in the next Chain loop, Chain 2
Step 2: Single Crochet in the top side bars of the Treble Crochet that you’ve already done – (Picot made)
Step 3: Continue to make (Treble, Picot) until you have 5 Picots made. Treble Crochet once more to finish the Scallop
Step 4: Skip 1 Chain loop, SC in the next Chain loop to anchor the Scallop
And that is it. If you wind up in a bind at a corner, with not the exact amount of rows, do a little “floating picot” as follows:
SC to anchor Scallop, Chain 4, SC in third chain from hook, Chain 1, skip 1 Chain loop, SC in next Chain loop.
Work corner: Copy your instructions for the regular scallop, but instead of only working 5 picots, you’ll work 7.
I got this pattern from here, https://cypresstextiles.net/2015/01/20/treble-scallop-edging-free-pattern/