...
After you selected one of the templates which was prepared beforehand for multiple files, you will see multiple input fields for attachments on the left hand side.
Once attachments are uploaded, at the bottom of attachments input fields, you will see the badge with information about the file (file name, size and a delete icon button) and where they are used.
What you should consider is that in the creative modal you can delete an attachment (with a delete icon) only if the file has not been saved yet. In Edit Creative modal you can see a badge with information about the file, but you can't delete it.
Please take note that you will need to upload the files field by field to ensure the right relation between the file and the destination can be saved.
...