Hello Hoang,
It is advisable to use your personal email. If you change your employer, you cannot take your certifications if you have no longer access to your work email address.
Have a look at the page and follow the steps:
https://learn.microsoft.com/en-us/partner-center/membership/ms-learn-associate
In the past, I had the same problem. Here is a solution similar to what I did some time ago: https://trainingsupport.microsoft.com/en-us/mcp/forum/all/link-my-private-learncertification-account-to-my/784be544-741f-434f-b3cd-2fd6a2fdb0ca
Does this work for you?
Best regards, Tobias