How can I connect two different accounts in two different instances?

We have a software that helps to create academic CV and share it with different organizations. This software has multiple instances and users might have accounts in those different instances. What we want to do is that to connect those accounts in different instances belong to same person. For example, I am a user in instance A, but also have another account in instance B. These are two different accounts belong to the same person. I want to connect those two accounts into one. That way, whenever CV is changed in one instance, we will update the CV of the same person in another instance.

How can I do that?