You can try using the resetperms plugin (install it in the omv-webui).. and reset your permissions on your folder... Set it to Admin read/write, User read/write, guest.. whatever you want... see if that helps. It should apply those permissions to all sub directories of a share.
There would be literally a 1000 page book on all the commands you could run (well maybe not that many, but it would be extensive). Here's a sort of "cheat sheet" I downloaded years ago... some of the commands have been depricated, and it's certainly not all inclusive.. but the "main" ones many will use (ls, cd, mv, and many others).. will work fine. I can't find a public link for it anymore, but It's on my Google Drive and you're free to take a look at it.
I could've sworn I tried the resetperms already and it not working but I just tried it again and I'm able to modify the folders in my median folder again. Thanks for the help.