These steps must be done very carefully. Technically, it would be correct to perform them in a cleanroom, but very good results can also be achieved without one.

Clean the glass of the optical unit with isopropanol and air.

Next, clean the protective glass of the sensor from the outside.

Now, use any suitable object to carefully lift the sensor's protective glass from the sensor. They will remain connected, but a gap will be created for cleaning.

Now the sensor and the protective glass can be cleaned from the inside.

Before reassembling, perform a visual inspection to ensure that the contamination has truly been removed. Conventional cotton swabs can leave fibers behind, which should be removed through additional cleaning if necessary. Streaks may also occur with particularly heavy contamination. In such cases, clean again.