Install and run Google Takeout Converter.

Then select takeout mailbox for transfer.

Choose Gmail saving option and enter new account credentials.

Finally, click on convert button to start the import process.

Export your emails from the old account using Google Takeout.

Import your emails into the new account using an email app. If you are using Thunderbird, you will need to additionally install the "ImportExportTools" add-on before you proceed.

For "Delivery method," select Send download link via email.

Select Create export.

In the email that arrives, select Download archive.

To download your Google data, follow the steps on the screen.