"missing input reference" showing for connecting the controller (joystick) for interactions in Unity

[Mariam]

I have been using a 2019 version of Unity for game development deployed to Hololens. My supervisor recently purchased XR VIVE Elite and, because Vive uses Open XR, I have to upgrade to the 2022 version of Unity. I was able to deploy the headset but encountered some challenges connecting the controller (joystick) for interactions from Unity. I keep receiving a "missing input reference" error. Interestingly, when I started a new blank Unity project, the controller input connected successfully, suggesting that something in the original project may be causing the issue. I've tried troubleshooting using suggestions from various forums, but none of the solutions have worked so far.

My questions are:

1. How can I connect the controller in Unity? Is there a documentation that can guide me? I also want to include hand interaction, if possible. 
2. Does MRTK work with the XR Elite? The project was initially developed with MRTK; do I need to remove the MRTK package before deploying to the XR Elite, or can I leave them as they are?
3. After deploying, it shows as a VR content. Do I have to follow this procedure to convert it to MR content [PC VR/VBS] VIVE Streaming MR with passthrough (Update Sep.19 2024) - Developer Support - VIVE Forum (htc.com)  to be able to see the real environment during game interaction.  
4. Finally, I still need assistance with setting up and obtaining eye-tracking data from the Xr elite device. We also have the Facial Ultimate tracker, and I would appreciate any help on how to retrieve data. Is there any software I need to install to access the eye tracking files?