Abbreviations
dc – double crochet
ch – chain
st(s) – stitch(es)Written instructions
Start off your wave fan edging by attaching your yarn at a corner of your previously completed project and chaining 3. You will then dc into the next 3 sts. Now, ch4. Turn your work. Insert hook into 3 ch from beginning ch3 and sl st. Ch 1 and turn work again. Now work 7 dc into the ch4 loop. Now work 1 dc into next 4 sts. Ch4, turn, sl st into post of previous 7dc/4ch fan. Ch1, turn again and 7dc into the 4ch loop. To go round any corners, just work 2dc, ch1, 2dc into one stitch at the corner, then create your fan as usual.
This pattern I found here: https://diyeverywhere.com/2017/01/19/watch-how-to-crochet-the-wave-fan-edging-stitch-video-written-instructions-/
And here is a video to a lovely lady making this edging.