Thanks Dr sahib, it was super easy to do.
The meter cover just pop out like a mobile battery cover.
Then the plastic cover can also be pop out by pressing 5 hinges . 2 on top and 3 and bottom.
Then both inside and out side of meter can be cleaned easily.
It is as good as new now.
There was also dust on digital meter.
I took some time and clean it very carefully from inside and the plastic cover.
Pics are attached for reference.