There are many different ways to fold a hackle feather to form a laid-back collar. You can use the back edge of your scissors to coax the fibers rearward or bend the stem through your fingertips which also works well. Or, you can use a cheap, easy-to-make little tool. All you need is a guitar pick or a similar piece of plastic, and some nail clippers.
Use the clippers to snip a triangular segment out of the tip of the pick. You should be left with a small cut-out, somewhere between 45 and 60 degrees, that looks about like this. To use the tool, anchor the hackle stem to the hook shank by either its butt or tip end, with its shiny side facing up. Place the pick’s cut-out on top of the hackle stem and pull or push in the opposite direction of how the fibers slant. Do this several times to lightly fold the fibers on either side of the stem back. Things don’t have to be perfect, just keep preening the fibers rearward as you take wraps with the hackle stem to form the collar of the fly.