from the DingDash help page
Posting Media
You can share videos and pictures by clicking the icon in the chat box that looks like a paperclip📎. You will be prompted to search for your file. After clicking on it, you will be given the option to post.
Unfortunately, at the moment, only files of 35 MB are able to load. Long videos are best shared from other formats, like YouTube, and then the link from YouTube can be posted on DingDash.
@Berrybunchfamily thank you!