How to merge one moodle server with another?

Hi all,
We have two moodle 4.1 servers, one was an experimental server where we wanted to test out some features. Now we wish to merge the two moodle servers into one where all information from experimental server needs to be added to the main server including courses, candidate history and grades. I have a few questions regarding this:

1. Same users have been enrolled with different usernames but same email id in the two servers. When we backup the course from experimental server to main server, how to merge these two users so the user progress remains intact.
2. What happens to users that are registered on experimental server, but not on main server when we restore a course from experimental to main server?