To add an intro and outro to your clip:
Open your clip in the editor by clicking the edit button.
On the right side panel, locate the Assets section.
Upload your intro and outro files into the Assets.
Once uploaded, click your intro asset and add that to the timeline at the beginning of your clip. Move the captions timeline forward to make space for the intro.
Click and add your outro asset to the timeline and drag that to the end of your clip.
Preview your clip to ensure the intro appears at the start and the outro at the end, with captions and other elements positioned as you want.
When satisfied, click export.
For a step-by-step visual guide, see the attached video.