There is a small dot of glue that was applied to the thread by the factory. This is to avoid having the lens fall off during shipping. You can try to scrape it off with a blade, then you should be able to turn the lens and adjust focus.
We also now have small quantities of sensors with the lens adjusted to 30cm - infinity, and we specifically asked the factory to not glue it, but those also have different lenses: 90 degrees, 120 degrees, or 68 degrees no-IR filter. On those you can adjust focus. Please see:
https://jevoisinc.com for the extra sensors
http://jevois.org/doc/Lenses.html for more info