@xionyus as I’ve told countless others that are new here with prebuilt systems, retropie is not a product you buy, but a hobbyist project that lets people build their own retro console. There is no firmware, there is no single programmer. It’s a mishmash of many different programs and projects by many different people. The retropie developers just brought them all together into a nice tidy little package. But it far from a full retail package.
The reason why we can’t help you is a lot of us know how retropie is supposed to work out of the box, with the base image. And is pretty simple. If something goes wrong, it requires your knowledge of what you did to figure out what’s going on. We have no idea what a 3rd party did, therefore can’t help.
Try starting over and enjoy the journey of how all the pieces work together, like how many of us started.
If you NAS is connected to the internet, then I guess it's a matter of configuring the firewall to allow access to the CIFS ports and making sure that file sharing is enabled for the internet interface. If you have a router in-between, you might need to forward the CIFS ports from the network interface to your NAS box.
Again, a configuration I strongly suggest against, since it exposes your NAS to the internet.