How to- and impact of combining users in Microsoft 365

Hi,

We have our domain "domain.com.ar" and bought the same domain name but with only ".com" ("domain.com") to operate in other countries. First we created a new users using the new domain because we didnt know the impact it will have in our business to change the mail address for old users. Now we want to merge them together. Our solution is to add "email address removed for privacy reasons" as alias and then set it as primary mail address, is that correct? So we need to delete the user we created to add it. And the problem is that we dont want to lose anything for those temporary accounts.

-Users:  tomas @ domain . com .ar

-Temporary users:  tomas @ domain . com

We want to know

1. How to merge them together and leave email address removed for privacy reasons as primary without losing anything from both users?
2. Impacts this will have.

Best regards,

Tomas Cossara