For front facing baby to see over, take the top ridge (connected to the straps), and turn it out once. Then turn it out again. This twists the whole thing, and the straps, twice. Then buckle it up.
If you only twist it once it will fold back in.
Re: back carry: what problem are you having specifically? Babytrekker is more my dd's papa's carrier, but I have done back carry sometimes.
General tips for how I do it: First do up the two arm buckles, buckling the strap to the hook on the SAME SIDE. You will have to experiment to see which hook is most comfortable - maybe get someone to help you adjust first time. Lay BT on sofa or bed, lay baby on it with arms under top ridge, legs above bottom, where they should be when carrier is on. Then sit in front of the carrier. Do up the velcro part that around your waist - do it high, above your waist. Then lean back, putting one arm at a time thru the armholes. Then sort of sit up, slowly, until you know for sure baby is secure in carrier. Have a feel back there for where baby's legs are. Good to go.
I think a big part of the comfort factor is having the carrier as high up as possible, and fairly tight.
Let me know...