Secure the hems with the pins then take the needle and put it underneath the folded part of the fabric
and bring the needle up as you pull through.
Tuck the knot and grab a little fabric underneath and pull through.
Grab the folded part and insert your needle thread ensuring that it’s the longer part and pull through.
Continue repeating the steps until you reach the end of the hem.
Flip it over and you should be left with a barely seen stitch.