Tried to uninstall Instagram and it ended up putting all my files in a LOST.DIR folder on my micro SD card and they can't be opened except if I add the .jpg extension to the name, then Photoshop will open them. There are 500 photos. So, I need to know what I can do to add the extension to 500 names, or at least convert them en masse. Thanks for any help.

All you need is a file renamer utility that can strut its stuff in batches. Most can, and one I have been using for a while is NameChanger (Disclaimer: I have no connection with MRR Software, other than being a satisfied user). That said, there are many alternatives, as mentioned in a.o. Quick File "Re-naming" Process.

Thanks. Pictures rescued!