Pitching an Idea

If an average person had a brilliant idea for a movie based on a true story what course of action should that average person take?

One can hardly call up Mr. Scorsese or Mr. Spielberg and say, “Hey man, you don’t know me from a hole in the ground, but I know of this story from the early 1900’s that has the potential to be as big as Forrest Gump.

“It’s got everything audiences clamor for: action, adventure, inspiration, obstacles, and humor.”

So what does the average person do? I’m not a screenwriter, and have no desire to be, but I would love for someone to tell this story. Any advice?

Peace, people