You write a letter to the congressman. In it include relevant facts about why he's applying, what he hopes to accomplish and what makes him special so the congressman can decide whether to endorse him. Also try to include anything about overcoming obstacles and such. It'll help. Make an appointment to meet with the congressman's aide or assistant and present the letter to the aide and basically " sell" yourself to the aide. If the aide gets on your side they will take the letter and talk to the congressman for you.. Hope this helps and good luck.