Check is there Backups tab in Create Droplet.
You need to see it as tab under Choose an image (e.g. Distributions - One-Click Apps - Backups (- Snapshots)). If you have it click on Backups tab and you should be able to select backup you want to make Droplet off.

If not, go to Images -> Backups, and Convert Backup you want to use to Snapshot. After that, in Create Droplet you will be able to select that Snapshot.

When you create a new Droplet from Snapshot (or Backup if possible) it will create new one, old will remain as it is and will work same as now.

I’m not sure for creating for Backup, I think I noticed it, but I didn’t used Backups for some time now.

Note that Snapshot costs $0.05/GB/mo as of October so don’t forget about that snapshot. :)