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 and click on the 3 dots and choose Edit.
2. Choose the take in which you want to add Captions, by clicking on the 3 dots a popup opens to show what you can do with your Take.
3. In the popup, click on Open Video Maker.
For now, Open Video Maker will add automatically Captions of your video but soon, you will be able to choose other Layouts. In the Video Maker, you will be able to choose between 6 kind of layout: Captions, Lower 3rd, Quote, Highlight, Intro or Split.
Soon, in the next release, the Lower Third will be available in the Video Maker, you will be able to select Lower Third applied for all Scenes instead of Captions.
On the Left sidebar options, in Style section, you will be able to change the Video Theme.