You have given very little information about your problem. Nevertheless, here are a few things you can try:
* If you are using the desktop version of Teams, try using the online version, the Teams web app (or the other way round)
* Try a different computer that uses Windows 10
* Try downloading a different file, i.e. from another assignment and see if you get the same error
* Ask the others who have access to that assignment if they have been able to download that file - it may be that there is a problem with the file or the permissions