'Send for marking' is an optional function in the Moodle assignment activity that has been added to allow the student and tutor to undertake a draft/re-draft process. You do not need to click on a 'Send for marking' button to make the file visible to the tutor for marking, you only need to upload the file. If 'Send for Marking' has not been enabled for the submission point then the student will not see the button on the file upload screen. It will be sufficient to upload a file.
If a file has uploaded correctly the filename will show on the file upload screen. It is always a good idea to leave that page and return to the assignment submission point to check that the file is visible there. It would also be wise to open the file that you see on this page to check that it is the correct file and that the file has uploaded in an uncorrupted format.
This is only possible if the tutor has set up the assignment activity so that deletion of files is enabled. To delete the assignment, navigate back to the submission via 'Edit Submission' and click on the submitted file. This will open a pop-up window with options to delete. You will then (if enabled) be permitted to add a new file. If this isn't possible, it may be that it either isn't enabled, the due date has passed or there is 1 maximum attempt and thus, the first submission is considered Final.
Microsoft Word® (.doc/.docx)
OpenOffice Text (.odt)
Hangul Word Processor file (.hwp)
Rich text format (.rtf)
Plain text (.txt)
Google Docs via Google Drive™
Microsoft PowerPoint® (.pptx, .ppt, .ppsx, and .pps)
Microsoft Excel® (.xls and .xlsx)