Dust in blower - how to access?

[As003]

Apologies if I am clueless about this stuff and get terminology wrong. Moved into rental and there’s a yucky dusty smell coming from the top vents of this. These top vents seem to be for the blower and it looks like many years of dust and cobwebs in the area settled on top of the firebox. I can’t for the life of me figure out how to access these vents to clean the settled dust. I found some screws in the door opening but that just took the door frame/rail off. It seems like the top vents are all one piece with the lower part. I was thinking a wire brush but the vents are thin and at a tough angle and that would just knock the dust around. Would appreciate any help! Thanks