You'd need to modify /etc/samba/smb.conf and add the folder you want to share, with a similar set of configuration options as the other RetroPie share
[...] [pi-home] comment = pi-home path = "/home/pi/" writeable = yes guest ok = yes create mask = 0644 directory mask = 0755The easiest way would be to enable SSH and use WinSCP to see the files on the RetroPie system, you'll have access to the entire filesystem.