I can find tons of videos on W&T while doing stockinette stitches but nothing on how to do it while you’re purling!?
Are you doing garter stitch by purling every row?
If so you could purl to the stitch you want to w&t, slip the stitch to the right hand needle, bring the yarn to the back, slip the stitch back to the left hand needle and then switch the needles in your hands. The yarn is in the front now, ready to purl and at the same time continue the wrap of the stitch.
If you’re doing stockinette but on a purl row, I think most of the videos cover the w&t from the purl side as well.
I really like German short rows which don’t use a w&t at all.