how to login again with another gmail and don't lose my projects in privious gmail could any one help me?
Export all you projects to your computer from your old email account on AppInventor, import them into the new one.
If you are too late to do this, then send @Susan_Lane a private message with the email addresses and the names of some of your projects, then she should be able to transfer the new email address over.
Yes, I can transfer projects if you have lost access to the gmail account connected to the projects. Just send me a private message (click my avatar and then the Message button) with the old address, new address, and a description of projects in the account.
If you have access to the account connected to the projects, it's better to export them and import into the new account yourself.