Sony ILCA-99M2 Manual page 366

MENU → (Setup) → [Cleaning Mode] → [Enter].
2
The image sensor vibrates a little to shake off the dust.
Turn off the product following the instructions on the screen.
3
Detach the lens.
4
Push the mirror lock lever (A) and open the mirror.
5
Use the blower to clean the image sensor surface and the surrounding area.
6
After you finish cleaning the image sensor, push down the mirror until it clicks.
7
Push down either side (B) of the mirror.