Well, depending on what VR setup you have I can either help you set it up or it might be impossible.
Portal 2 in VR runs on a PC (a pretty good gaming PC) connected to the headset either through a cable or wirelessly. If that’s the setup you’re using, it shouldn’t be too hard to figure out.
If you have an Oculus/Meta Quest and only play standalone (that is, no PC is involved, everything runs on the headset), then I’m afraid that’s not good enough for Portal 2 or Half-Life 2, though there is a VR port of the original Half-Life. All you’d need for that is any PC (even potato quality) and a USB cable.