I had a dress that I had already taken off the sash for a necklace last week and figured the straps would be perfect for this necklace since they had the length adjustments on them.
Here is what I did:
Cut a piece of material in the length and width you want your bow. Fold one end in and then the other end in, slightly on top of each other. Mine is a bit smaller than the one from Urban Outfitters. Lay the sewn strap on top of the bow, which will be laid on top of a small piece of fabric to tie around both. You can make yours more like the Urban Outfitter one by making your bow bigger so that it hangs lower.
Tie the small piece around the bow and strap securing them both. Now using your scissors, cut the tied part down so that its not seen from the front when wearing this.
This is what its like when its longer.