Press X (Square on PlayStation, Y on Switch) to switch to the path a little further back in OlliOlli World and you should see a big “Gnarly Route!” icon at the top of your screen. Then, grind the big rail to gain some speed, jumping and switching rails when necessary.
How do you do manual OlliOlli?
To manual in OlliOlli World, you just need to press the Push button and tilt the left analog stick to the left or right just as you land from airtime onto the ground. You’ll perform a better manual if you time it precisely as you land, but you risk messing up if you press it too late.