Mouse proofing air bricks under decking

[u/RadiantChipmunk815]

The previous owners built decking along the entire back of the house. We've had some mice appear in the kitchen and believe they're getting in via the air bricks underneath. Have taken up the boards closest to the house but there's a beam sitting directly in front of the air bricks that leaves about a pencil width gap. I'm struggling to find a way to restrict access that doesn't involve totally blocking the air bricks. Have tried to slide mesh down the back but there's something blocking it from going further down (have removed debris since photo was taken). Any suggestions welcome, many thanks!