I recently acquired a Oculus Rift CV1. One of the touch controllers was missing the cap in the middle of the thumb stick. Unable to find just that part without buying another controller I decided to make one. After you print this you can use super thin double sided tape or you can glue it on. whichever you prefer. I used the super thin double sided tape. This is the tape I had around the house.
https://www.amazon.com/gp/product/B09BB9DCR3/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
After I printed the replacement cap I placed it on one of the sides of the tape and cut around it with scissors. Then I removed the paper on the other side of the tape and placed it on the thumb stick.
The author marked this model as their own original creation.