Oh, so sorry, this is annoying. We are still working with the factory to make sure this does not happen in the future. From the sensor manufacturer (OnSemi), we receive sensors with a piece of yellow tape on top of it. This is so that it will not get scratched when the pick and place machine takes it out of the tray and places it on the PCB. Then, after the board is soldered, the tape has to be removed. On the samples we have looked at so far, we have found that sometimes indeed there is some dust which was under the yellow tape. In such cases, the sensor should be cleaned before the lens mount is added. But I guess your unit was not cleaned well.
There is a protective piece of glass on top of the chip. So there is little risk of damaging the chip. You should clean the glass with any microfiber cloth that you would normally use to clean glasses, camera lenses, etc. I would try to avoid any chemical at first, but if needed you could also use a small alcohol pad or iPhone wipe, and then wipe out all the alcohol with a microfiber lens cloth.
We have used these here in the lab to clean expensive DSLR cameras and lenses with good success: