It's the same as the front tie - back to front. So, if you have help, put the middle of the fabric across the middle of your back, cross it over your chest and pass it up over your shoulders, cross it again and tuck the long ends down under the bit across your back then bring them to the front and tie or cross and pass to back and tie as you usually would. Then take the outer strap down, have your assistant put bubs in, exactly as you would if they were on your front, pull the strap up and have the assisstant spread all the straps so you're both well supported and you're good to go.

If you don't have help it's trickier and possibly nonsensical but i'll try to explain. You need a relatively cooperative toddler - the first few times i did it on my futon so if she fell it's be fun and not agony.

Lay the HAB open and spread on a bed/couch (something not too low) and stand in front of it, stand so you're next to the middle of the HAB fabric. Pick bubs up and hold him on your hip, then lean forward as you pass him round under one arm so he's on your back as you lean forward. Hold him stead with one hand and stay leaning forward - if your back is parallel to the ground he should be fine with one hand steadying him unless he's really wriggling in which case it might be better to get help or give him a few minutes to settle. Using your spare hand pick up one side of the HAB, near the middle, then support bubs with this hand, still holding onto the HAB while you grab the HAB further down with the other hand. You should now have the middle section of the HAB stretched between your hands, passed over your back/bum. Now pull it up one hand at a time until the top hem is across bubs back under his armpits. Once it is spread over his back like this pull it TIGHT and tuck the ends between your thighs to keep it tight - your hands are now free. Carefully take the right side out from between your thighs and, keeping it tight the whole time, pass it across your chest, over your left shoulder, over bubs lef shoulder, across bubs back and between bubs legs, bringing it back under his right leg, round your right side. Tuck the end, still tight, back between your legs. Repeat the process with the other side, so you have both ends between your thighs again. Now, the tricky bit (!), i use a wardrobe mirror to help, feel aong the straps and make sure everything over bubs is as flat as possible - it tends to bunch, especially between the legs. Once you're happy it is all good, stand up slowly and as you do, "hump" bubs up higher, as you would a rucksack you were shortening the straps on, and pull your ends (which are under bubs bum remember) to hitch him higher. Then tie the ends, make sure your shoulders are comfy and off you go.

I hope that isn't just garbled nonsense!

Bx