Push the yellow joystick on your left hand forward to fly in the direction you're looking at.
To fly straight down, you can press the yellow joystick like a button. To fly straight up, press the purple joystick on your right hand.
Flying is a very versatile way of exploring your model, but if you're prone to motion/VR sickness, we recommend using teleportation only.
Flick the purple joystick on your right controller left and right to ratchet left and right.
Push and hold the purple joystick on your right controller forward to begin teleporting. You'll see a target shoot out from your controller.
Point the target to the spot you want to go to, and release the joystick to teleport there.