Get a piece of window screen that is larger than the hole the bats are using. You want to tack or nail it over the opening so that it makes a one-way door. The bats should be able to push the flap open to get out, but they will not be able to lift it or crawl under it to get back in. Then wait a few days. This will give all the stragglers a chance to vamoose before you cover the hole permanently. Next, put up a bathouse somewhere not too far away so your little friends can still spend their evenings eating mosquitos for you.