You can manually transfer emails from one Yahoo account to another but this method does not work if you are using free Yahoo Mail Service. However, you can perform Yahoo to Yahoo migration without any hassle with Advik Yahoo Backup tool.
Eldfall Chronicles The software can quickly export Yahoo Mail folders to another Yahoo account in just a few simple clicks.
https://3dtrcek.com/en/3d-filaments/pla-filaments It preserves data integrity and folder hierarchy during migration. It can move complete mailbox folders at once.