Tap your preferred Apple Store to be taken to that Store's page. To book a Genius appointment, scroll down to 'Genius Bar'. Tap it, and you'll be taken to a menu in which you'll need to pick your affected product. Scroll through to your preferred time and date until you're happy, and then select it. Schedule Apple Genius Bar Appointment
Furthermore, do Genius Bar appointments cost money? A Genius Bar Appointment doesn't cost anything. That is, it doesn't cost you anything to show your device to the genius.