Thanks for asking question! You may refer to this article: Export and import Azure Notification Hubs registrations in bulk which explains how to perform a large number of operations on a notification hub, or to export all registrations, in bulk for the scenarios like tag update in which it is required to create or modify large numbers of registrations in a notification hub.
Check: How can I update multiple device registrations on Azure notification hub
Let us know if you have further query on this.