What is the best way to procure assignments while migrating the space from confluence cloud to serve

[Vineet Kumar]

Hi, I have to migrate confluence spaces from Cloud to Server, The issue is, for the users, the usernames are different in cloud as well as confluence server but the email id is same. So, If i am importing the space to server the users are loosing the assignments to the wiki pages. e.g. creator of the page is appearing empty. 

May i know what is the best way i can procure the these assignments while performing the imports. All the users are present in the target confluence server with the same email id but with different usernames.