Clear videos are not so easy to come by for this. The idea is to look over your needle to the purl side, count down 5 sts and pick up the purl loop and knit it together with the st on the left needle. The idea is to make a welt or tuck or fold in the knitting. See if this one
helps out. Bear with the beginning and I'll see if I can find the good Eunny Jang video for this.