How do I restore the default repositories?

My zorin os 16 pro was not getting updatte. So I cleared all the links from sources.list.d How can I restore them?

That is not the proper solution to the problem.

Fortunately, your Zorin OS sources should still be intact in your /etc/apt/sources.list

You can plug in your Installation Media for Zorin OS (LiveUSB) and transfer over from it:

zorin.list
zorinos-ubuntu-apps-focal.list
zorinos-ubuntu-drivers-focal.list
zorinos-ubuntu-patches-focal.list
zorinos-ubuntu-stable-focal.list

And as a Pro user, check for any Zorin related Premium files in there.