You have to be in supercruise. There are two ways to scoop: you can face the star, slowly get to the spot where your heat is around 100% and park there (zero throttle) - it's a slower way, but you don't overheat; a faster way is to line up with "horizon" of the star and keep moving around it, but you will overheat while doing it, so it might require a few passes with cooldown time in between.