How to adjust a roll forming machine's span?

How to adjust a roll forming machine's span?
How to solve a zinc coated roof sheet roll forming machine sample's surface not good problem?
During running first piece of the pure no color zinc roof sheet surface is with dot, or with wave problem, how can we solve this? We should test the machine by several pieces of zinc coated sheet slowly, and to check one station by station by our eyes to find out which place causing the problem. We only can solve the problem after doing this work.
Second, the working shop engineer discuss the problems and work out another good solution according to the actual affection.