After you upload your video on the Create page, you will have the option of trimming the audio by clicking/dragging within the media bar below the preview panel:
The audio clip that will be included is highlighted in aqua.
Also, check out this video to walk you through selecting the perfect snippet, too:
When is support available?
Read this link for support hours: https://support.wavve.co/en/articles/5373873-when-is-support-available-to-help-me