Pre-nominating a round is an important part of the handicapping process, ensuring that people cannot manipulate their handicap to gain an advantage in an upcoming event or tournament for example.
If it's a social round for the intention of maintaining and updating your handicap, then it needs to be nominated at least 24 hours prior to play.
If you are submitting the round as part of your first 3 cards for handicap the nominate button will not appear in your membership dashboard. You can click on "submit scorecard" and directly submit one of your first three scorecards.