You can transfer Email from One Gmail Account to Another in a manual way or professional way. For the manual way, enable POP in the old Gmail account, then link it to your new Gmail account via "Accounts and Import." Gmail import all your previous emails to your new inbox. Alternatively, you can manually send them over (forwarding) one at a time or use Google Takeout, then download & re-upload the data.

The manual method is slower, risk you might lose data, and won’t work for labels & filters if you use one. Additionally, the larger the account, the longer it will take to sync.

Get an expert's advice on taking a backup of your Gmail account before you do any transfers & for that, you can try MigrateEmails Gmail Backup Tool and it can make easy for you and solve your question of how to migrate emails from Gmail.

1. Download MigrateEmails Gmail Backup Software from the website.
2. When you open the tool, you will login to it with the credentials of the source Gmail account that you want to migrate emails from
3. Select the email folders (Inbox, Sent Items, etc.) that you want to migrate from your source Gmail account.
4. Select Gmail as the destination from the drop-down selection.
5. Enter the credentials of the destination Gmail account that you want to migrate the emails to.
6. Use free advanced filters to filter on criteria, such as date added or email categories, so that only the emails you want to transfer will go to the destination account.
7. Start the transfer, and the tool will securely transfer from the source account to the destination Gmail account.

Know More: https://www.migrateemails.com/blog/transfer-emails-from-one-gmail-account-to-another/