Go to Tibau do Sul city, 6 km away from Pipa Beach. Go to the beach towards the little 'quiosques'. Look to the ocean straight ahead and you'll see it. Paddle off the beach at falling tide or take a boat.
Try to get a boat to take you there. If you're paddling out, make sure you do it at falling tide and return at rising because the rip is strong due to the spot being located at the mouth of a lagoon.