When it comes to accurately throwing a Bowie knife, your first lesson is that you're going to need practice! Now if you add in these tips as well you should be hitting your target within the first hour! There are many different styles of throwing as well as different stances. To simplify things for now, we are going to review throwing the blade by the handle.
Grip the blade by the handle with your dominant hand. Hold the blade vertically from the ground straight up and down. Stand about 15 feet from the target with your legs shoulder width apart and with you dominant side forward. Wind up by drawing back your throwing arm while keeping the blade straight. The going forward your throw should be similar to a baseball pitch minding the blades straightness. Release is almost natural but you can look for when the tip of the knife comes into line with the target. Aim for a smooth release with no extra wrist action, the knife should almost slide from your grasp.
For starters a good turn and a half through the air is what you should look for in your throw. You can try adjusting the amount of power you use but in many cases it's easier to take a half step forward/back.
Hopefully this helps you have a fun and successful time at the throwing range! Remember to stay safe and never throw when someone is in front of you on the field!