How we integrate Erpnext with KOHA Library System and when we create data in erpnext then that data going to fetch in KOHA Library System.
if koha has a web api , you can use frappe webhooks feature to send data to koha apis
https://frappeframework.com/docs/v14/user/en/guides/integration/webhooks
you can select v13 this doc is for v14
idk about koha but i think this the koha api .
https://api.koha-community.org/