If you found our default csv importer extension does not meet your requirements, then you can try with WP All Import plugin to import your Books in the csv format.
How to import custom fields quickly:
1. Go to All Import › New Import.
2. Choose the import method (i.e., upload file, use a URL, etc.) and select the file that you want to import.
3. Select the custom post type that you wish to populate (i.e., the one containing the custom fields).
4. Map the incoming data elements to their corresponding custom fields using the Drag and Drop interface.
5. Run the import.
