If steamvr is already open it will say play in vr when you click the play button.
what you need to do to play no mans sky in vr is turn on your vr headset and get set up before starting the game.
No mans sky - vr mode please select the game in gog galaxy, click the customization button (next to play) additional executables no mans sky (openvr). Compatibility may vary between vr headsets, this guide might be helpful.
In the game properties put -hmdenable 1 in the launch options.
Here you go into the top left option to change it yourself, if you scroll down to the bottom you will see bindings uploaded by others.