To transfer a generated video from a Synthesia account to a new one:
Access your old account and go to the video overview page.
Go to the top right-hand side of your screen and select Publish or Published.
In the pop-up that appears, ensure that Public Access and Allow Video Duplication toggles are set to On.
Copy the public share page link.
Switch to your new account by signing out of your old account and sign in to your new one.
Open the previously copied share page link in your browser and select Duplicate video in the top right corner of the page to duplicate it into your new account.
You can now edit this video like any other video.
Optionally - Go back to your old account to disable Public Access on the video.
Notes:
Only generated video can be transferred between two Synthesia accounts.