You mean the In-VR Steam menu, right?
You don’t need to do anything for that and I think you even can’t.
I would need to double check if it always works while Steam is running but especially when your game is launched from Steam you will be able to bringt up the SteamVR dashboard without having to do anything since it is a functionality from SteamVR that has nothing to do with your game.
And if I remember right that if you have a non-Steam game it will simply say that you are currently running a non-Steam application, I could be wrong on that point though.
TL,DR: We didn’t need to do anything for our Steam game to be able to show SteamVR dashboard since it is a SteamVR functionality independed of your application