For some opportunities, the buyer may require you to submit an Intent to Bid which will look something like this:
If you've already submitted your Intent to Bid but you no longer wish to bid, you can go back to the opportunity page, and change your answer from Yes to No.
Note that you will not be able to change your answer if the Intent to Bid deadline has passed. In this case you do not have to take further action unless further specified by the buyer. The idea behind declaring your Intent to Bid is to allow the organization running the bid to get a rough idea of how many submissions may be coming in. If the Intent to Bid period closes and you do not submit, it should not make a difference.