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To start, you'll need half your sts on needles 1 and 4 so if they aren't distributed this way, move the sts around on the needles so that they are. Start at the beginning of round on needle 1 and knit across, then turn and purl back across needles 1 and 4 working all sts onto needle 1. Now you have the heel sts on a single needle and you'll be working the heel flap back and forth on this needle in stockinette stitch with 3sts on each end in garter stitch (k3 at each end on every row). Work as many rows as you have sts.
For the heel turn, put in markers that divide the heel sts in thirds so if you have 15sts, mark off every 5sts. On a RS row, knit across 5sts of group one and then 4sts of the middle group, ssk, turn slip one, purl across 4sts, p2tog and turn. Continue in this manner to work across the middle group of sts, decreasing at the ends and slipping the first stitch after the turn. Each time you decrease you'll be working one stitch from the first or the third group together with one stitch of the middle group of sts. Keep doing this until you used up all the sts in the first and third groups and you're left with the middle group of sts only.
The details are different but the idea of the heel turn is the same as shown here.