1.Quick start guide, FiiO Control APP download link of RETRO NANO

Quick start guide download link
Click here

USB DAC driver
When the RETRO NANO is in UAC mode, no driver is required in the computer. Just select the RETRO NANO as the default audio output device after connecting it to the computer.

FiiO Control App download link
Android version: Click here
iOS version: You could search and download 'FiiO Control' from the APP store.