Your players will start on whichever map that you place the "Players" flag. Just create a new blank page, set it up as you like and drag the banner to it. If you never plan on using the module's default start page, archive or delete it. If you're talking about the image that appears on your game's launch page - the one that the players see before actually entering the game - then you can simply hover over the image, select "Change Image", or just drag and drop an image from your PC to replace it.