Here are some things you can do if you are unable to access a specific file in a Teams channel:

1. Check if the file has been deleted or moved to another channel.
2. Make sure you are signed in with the right user account.
3. Ensure you have correct permissions to access the file.
4. Check if the file is locked and that you have edit access.
5. Look for another shared location where the file may have been moved.
6. Ask a system administrator or the file creator if he/she can share the updated version of the file.
7. Try again after a few minutes.