So here's there the front part of the rainbow sock with toes ( I personally like the toes part! )

& here's the back part where the heel is .

First , you have to cut off the toes part .

Just the tips though , you want your fingers to be able to have seperate

& so this is what it'll look like :D

Now flip it over to the back so you can work on the heel bit .

Lay it flat , the heel part will tend to stick out .

Just fold it in .

Once you've fold it in & are happy with how it looks , it'll look something like this .

Then sew the gap shut however you like .

Ok , so I'm not good at sewing , but heck it was an attempt :p

Just as long as it's sewn shut & doesn't stick out , it's all good (:

After sewing ;

It'll look like this .

It's not perfect but it works .

& there you go :D

Good luck!