got it! OK, if you go to your one drive app.
You have two options here.
option 1) make the files avaliable in one drive offline
go to one drive
tap on files
then tap on the 3 dots going down next to the folder you wish to make available
a pop up screen will appear and you'll see a selection for 'make files available offline
option 2: download the files back to device in bulk
navigate to the folders in concern, tap on them to open
for example I have camera roll and screenshot.
tap and open your folder in concern.
then tap and hold on one of your images/videos until your screen displays selected.
tap all of the items you wish to download
then tap the arrow going downwards on top of the line in the top right of your phone.
you'll then need to select a location on your phone to download them.
hope this helps



