First step is to be sure that your ISP is delivering the service. You can check that by plugging the fiber cable (coming from the fiber box) directly to your PC as this should give you an access to the Internet already. If that is not happening you should discuss the lack of service with your ISP.

If fiber connection is running smoothly you may still ask your ISP to update MAC address (also called ‘physical address’) of your new router. Then simply follow the steps in ‘How do I clone my PC MAC address to the router?’

https://eu.dlink.com/se/sv/support/faq/covr/how-do-i-clone-my-pc-mac-address-to-the-router