Search for the "Seethru" prefab on the search tab
Drag and drop the "Seethru" prefab onto your Avatar's scene file
Make sure the Armature hierarchy names are correct
Position the "Seethru" prefab exactly to where your Avatar's viewpoint is located
Select the "Seethru" prefab and drag the "Parent to Neck" object to your Avatar's Neck bone and a pop-up will appear saying "This action will break the prefab instance. Are you sure you want to continue" just ignore it and click "continue"
We will also need to add the head as a fixed joint for this object's rigidbody component
Click on "Add Component" and type "rigidbody" and add the values for the Rigidbody component as seen here
Last step is to add the emotes and gesture animation to your Avatar's animation Override component
Has 3 modes: Red Dot Sight mode, Scope Reticle mode, and HUD mode (The latter two has 3 variable zoom modes)
Scope Reticle Mode - A Sniper scope type reticle right in front of your viewpoint, less effective at seeing through walls
HUD Mode - This uses Error.mdl's EHUD shader, this is the most effective at seeing through walls
Red Dot Sight mode - Just a simple red dot sight