You may update the case that had been submitted to UCS, for any changes related to the following :-
1. To change the ‘Subject’
2. To change the ‘Type’
3. Add comment and attachment

Please do the following:-
1. Sign in to the UCS portal.
2. Click My Support.
3. Click the Case Number to open the case details.
4. Make the changes or click 'Add Commen't button to attach the file.
5. Click ‘Update’ button.

Please refer to the guideline with the screenshots by clicking this link.