If you have aluminum arrows, just heat the end by the insert a little bit, and turn the insert where you need the broadhead to be. Make sure it lines up with the fletching
Also it is a good practice to spin the arrow with the broadhead on to make sure it doesn't wobble. You can do this by setting it on a corner of a table and spinning it. If it wobbles don't use it. It will not shoot straight.
If you have carbon arrows the best way is to buy some rubber O-rings. They should sell these at most sporting goods stores. Then you just turn the head until the blades line up and the O-ring keeps the head tight.
I do this with all of my arrows. Have for years. If this is done correctly all your broadheads should shoot exactly the same.