Hello @apichaya-s ,
You can safely use the email address with both GitHub and GitLab, none of your projects or configurations are going to be removed. What will happen is that (taken directly from the message above):
- You will no longer receive email notifications from this account (the one that was logged in before).
- Issues won’t be automatically assigned to this account anymore (the one that was logged in before).
In the end you are going to have an account and organization for GitHub and one for GitLab. It is not possible to use the same organization for GitHub and GitLab projects at the same time.