I pushed a controller button in PeriopSim and there is a popup menu showing

SteamVR and Mixed Reality menus can be displayed while running VR. Dismissing these menus can be done by a second button press.

Depending on which head set and which button was pressed will indicate which button to press again to return to PeriopSim.

Windows Mixed Reality Headset

If a row of 5 or 6 buttons is displayed on screen press the Windows button on the controller (small circular button located midway up the handle of the controller.)

If a large windows showing the Steam VR logo is displayed and the PeriopSim OR is not visible aim the laser at the SteamVR window and press the trigger button.

HTC Vive

Press the power button on the controller (small circular button located bellow the trackpad) to return to PeriopSim.