Now I want some of these records to be searchable from a specific library instead of "All Libraries"

Do you bibliographic records have items attached? The item record is where the library information is stored. It sounds like you need to set the "Permanent location" and "Current location" values in the item records. If you can put together an SQL report to return the set of records you want to modify, you could use the Batch Item Modification tool. -- Owen -- Web Developer Athens County Public Libraries https://www.myacpl.org