Tap Settings button on the left side of the playback screen.
Select Post Processing in the Video tab.
Activate Post Processing and select 3D Mode.
If you activate 3D Mode, you can configure Input/Output, Resolution and Swap Left/Right.
Input : Monoscopic, Output : Side by Side
Input : Side by Side, Output : Side by Side
Once 3D Mode you want is activated, you can enjoy video files in three dimensions with your VR device.