Bats roosting behind a shutter - How to exclude them / seal shutters

Bats roosting behind a shutter on the rear of our house. I have no problem with the bats themselves, but they are shitting all over our deck! We definitely want them gone, and plan to kick them out around mid-August once any babies they might have will be big enough to fly.

They are only behind the one shutter. I know I need to remove and sanitize it. I also know I need to seal it off (and all of the other shutters) and prevent them from returning. But I can't find anything specific on how to do that. In my research, I've seen people talk about using cedar shanks, black poly screen, a foam backer rod, etc. I'm not sure what would be best, or exactly how to go about doing any of them.

Any advice or videos you can point me to would be greatly appreciated.

I wish we could just remove the shutters, or have them stick out a few inches, but we have a crazy strict HOA.

Thanks!