If files where stored on SD card you can unmount SD, plug into PC and download and run a software called Recuva.
It may or may not be able to recover most of it.
Whether on a phone or computer when you "delete" something it just marks the data as being ABLE to be overwritten; but if it has not been overwritten the data is still recoverable.
Now if this was on your internal storage then your phone would hav eto be rooted to be able to run any sort of undelete software on the phone to attempt to recover.
Why oh why by 2017 have people not figured out that they need backups.