You will put duct tape all the way around your body covering both breasts. then you will take a condom, fill it with water and freeze it. When it has frozen you will that it inside yourself.
Take some rubber bands and wrap your tits in them. Put some “chip clips” on your nipples as clamps. After about 20-30 mins take everything off and snap your nipples several times with the rubberbands. Make sure you do it hard enough to leave marks!