What you needJewelry Wire.
Take a wire and make a loop at the both ends using a looping pliers. The length of the wire depends on your choice. Make six pieces like this.
Now take two looped wires and attach them on the ends of the chain. Then take a jump ring and join the two loops using the jump ring. Now take another jump ring and attach on the loop and then take two more pieces of the looped wire, then attach them right above the previous ones. Keep doing until you are happy with it.
You can also use just one looped wire to make a very simple one.