I followed below instructions given in NGL Forum and it works. you need to reindex after deleting 2 folders as mentioned below.
check u r able to search books using SEARCH CATALOGUE in ngl client. if its not working then close ngl server and delete below 2 folders. (delete only data folder, dont delete anything else)
NGL3 --> Authority_Solr --> Delete Data folder
NGL3 --> Bibliographic_Solr--> delete data folder
Dr. Yesan Sellan, PhD