How to update datetime field on button click?

 I have a table in sql that has a "DateSubmitted" field that uses (getDate()) in sql to populate the column with the current date and time when the row is inserted.  That works great for the insert, but I also need to occassionally allow the user to update their data, so I want to update the DateSubmitted Field with the current date and time.  How do I do this? 
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