Someone may have provided a URL or a UUID of a player to you, but you can't see it when searching in the dashboard.
The most likely possibility is that the player belongs to a group that you do not have permission to access. Alternatively, you may be looking in the wrong group. To switch groups, press Group > Change Group
Feel free to contact Vidyard Support to check your permissions, but ultimately your Admin will need to ensure that you are in a role within the group that has the correct permissions to do the job required.