Unfortunately, I don't think it's possible to play Free Fire Mod on a Vive headset. The game is only available for Android and iOS devices. However, there are many great virtual reality games available for the Vive headset that you could try.
It does not appear that there is a version of the game Free Fire Mod for the Vive. You might be able to find a compatible version for a different VR platform, but it does not look like a version exists for the Vive.