The Roblox beta version does not support virtual reality and you will have trouble setting things up if you use it. After you uninstall the Roblox beta version, install the regular version of the game with VR support from here. After that, you can complete setup in your VR headset using instructions below.
Full Answer
Oculus Rift:
How To SETUP & USE ROBLOX VR On Oculus Quest 2 – 4 STEPS
Roblox isn’t available as an Oculus Quest or Quest 2 game, so you need to connect your headset to a PC using a link cable. Once you’re connected, you can enable VR from the Roblox setting menu. Once you’re connected, you can enable VR from the Roblox setting menu.
Method 1: Running Roblox on Quest 2 Using a Link Cable
To enable your VR experience with Roblox, you'll first need to make sure you've installed Roblox (http://www.roblox.com/download) and then follow the steps below: Please ensure that your device is properly connected to your PC and VR Mode is togged to " On " within the in-game settings (Menu>Settings>VR>On). For more details, see How ...
Open the Oculus App on your computer and select the gear icon in the upper right. Select Gear Settings. Select General on the left menu. Toggle the Unknown Sources setting so it appears as a check instead of an X. Confirm your selection to enable this setting. Select Play on a Roblox game: http://www.roblox.com/games.
To bring up the System Dashboard, press the System button on either controller. Note: When you quit the SteamVR app, the controllers will automatically turn off. The controllers will also automatically turn off after being idle for a period of time.