The recommended procedure is to sous vide, then chill the bag in ice water before transferring to the fridge. This minimizes time in the food danger zone. Then before serving, put into the immersion bath again for a short period of time to warm the steak up to room temperature. Finally, sear for a couple minutes on each side and serve. With thinner cuts of steak - like this flank steak recipe - you can reheat entirely in the searing step.