When you look at a p2tog decrease from the knit side, the stitches slant to the right, just like they do with a k2tog decrease.
Insert the RH needle purlwise into the next 2 stitches on the LH needle.
Position the needle like you were purling a single stitch, except insert the needle through two loops. You’re on your way to working a single p2tog decrease on the wrong (purl) side of your knitting.
Wrap the yarn around the RH needle.
Perform the action just like you were working a single purl stitch.
Pull the RH needle through the loop.
Again, purl the 2 stitches together as if they were 1 stitch.