Please note: adding a 3rd lower titling is possible only when styling without captions. You can't use both - a 3rd lower title and captions in the same video.
1. Open the relevant video.
2. Click on the 3 dots and select Style your video.
3. Go to Theme and choose a lower 3rd title.
4. Now you can edit your 3rd lower title's information.
5. Click on the Make Video green button to apply the changes.