Thanks for reaching out to us!
It looks like this video was uploaded by your colleague. In order for you to download the transcript on any video that you have not uploaded yourself, the video must be shared with you with the 'Full Rights' permission. The 'Full Rights' permission level gives you the ability to download, duplicate, and edit the video, as well as the ability to export the comments and reshare the video.
The best thing to do now, is to reach out to your colleague and ask if the sharing permission can be changed to 'Full Rights'. The person who uploaded the video can change the permission level by clicking on the orange 'Share Video' button on the top right of the video, and then clicking on the pencil icon next to your name.
For more information about how sharing works, check out our video tutorial.