I have submitted the DS 160 online application but couldn't pick appointment date because the conference would have been over. I have submitted another DS 160 application form and have schedule an appointment but for a different purpose. Will the embassy use the information on the previous application for my interview or the newly submitted application. Are they going to discard the previous application or still going to consider the information on it
The previous application is completely irrelevant and the consulate would only consider the information in your latest application, since you never visited the consulate for an interview for the previous visa application.
Of course things might be different if you've admitted to genocide or similar on your previous DS-160, but I presume that's not the case.