Hi Zoe, to start sewing, you first need to bring the yarn end on the right arm out two rounds below the last round you crocheted. So you take the yarn end on a yarn needle, insert it into the tiny hole where you closed the last round, and bring the needle back out two rounds below. This is the point a. Then you insert the needle into the body, at 3 rounds below the neck, you go through the entire body to the other side, and come out in a stitch, again at 3 rounds below the neck. You then insert the needle in the left arm, in a stitch 2 rounds below the last round you crocheted there before, bring it through the arm and out again in a stitch on the other side of the arm, at the same height. You then insert your needle into a stitch one of two rounds below the point where you brought it out, and go back through the arm and the body. When you bring your needle out of the body, you then insert it into the right arm (1 or 2 rounds below point a), bring it out on the other end, bring it back into the right arm (1 or 2 rounds above). At the end, you bring your needle out again at point a. You then make a knot with both yarn ends (the starting and the ending yarn tails) and hide the yarn ends.

You can also play around a bit with the exact placement and sewing of the arms, the instructions are just the roadmap, you can make the journey your own :). I hope it works out!