how can i retrieve the files i've accidentally deleted in file manager?
Unfortunately you can't unless your web hosting company takes off site backups.
Normally they ask for confirmation before removing the files. If you accepted the confirmation, they are "removed".
In case you want them back, you can kindly ask your host, but better would be just to use the files from your last backup which shouldn't be too far -- at least I hope
|Nico Lawsons - Quality Web Hosting at WiredStorm
|cPanel with Softaculous and 24/7 Email (Ticket) Support & Live Chat
Only chance you can get it back is if your host takes daily backups other then that they are gone forever i'm afraid.
I dont think it is possible, i suggest you create a next time after every month so even if you loose any files you accidentally deleted you can always recover it.
Follow me on Twitter: @hendricius