Export all items to a Mac or PC if the app is not working:
Even if there is ever an issue with the app, or for any reason other export options do not work, or you cannot access the app, you can still Export all your files to a Mac or PC:
On Mac, plug your iPhone into your Mac and open Finder. On the left hand sidebar, select your device, then choose Files > Locker > Data. Drag this folder onto your computer to save it.
On PC, download the iExplorer app from https://macroplant.com/iexplorer. On the lefthand side, choose your device, then Apps > Locker > Documents > Data. Drag this folder to your computer.