Just put her down on a flat surface no pillows of blankets or sheepskins or anything, straight on her matress, elevate the end a little bit (assuming she is in a bassinet?). Try it at nap times first, and if you are concerned, keep checking on her (I did lol) but you can get breathing monitors and things, but we never bothered.
Make sure her head is on the side, and move it to the other side every so often if she sleeps for ages.
I found Charlotte was able to move her own head a lot earlier than everyone seems to say and she was very good at getting herself comfy.

I was concerned to begin with, but soon realised this is just how she was - she was prosterior and I am a tummy sleeper (until I was almost 30 weeks) so I suppose she was used to sleeping on her tummy? lol
Anyway, give it a go, you may find she sleeps much better and for longer.

HTH