I need to restore my phone to an older backup version.

I need to restore my phone to an older backup version. I've deleted the most recent ones to have the correct one first, but when I go to select it, it doesn't show up, but under the dropdown menu it says the name/timecode of the one I need....When I was deleting the most recent versions, the one I needed had a lock next to it, which I'm assuming is the problem.... Help!