1. Open the HunieBee and go to the GIFTS tab.
2. Purchase the BAG OF GOLDFISH for 200 munie. (if it is not there, progress through the game to get to the next day. The store will reset every day)
3. Go to Dawnwood Park, open your inventory and grab the fish. Drop the fish into the garbage can that appears on the right of the screen. Leave the date and Momo will appear. (I think you can also have your date, then before you go to find another girl, throw the fish away. Don't try to throw the fish away and then have a date.)