I am new to Lean Six Sigma and have a question on best approach to determine the root cause of a defect that is occuring at one specific point of our process. It is at the cut to length operation. It has came to light due to a customer complaint.

I am new to Lean Six Sigma and have a question on best approach to determine the root cause of a defect that is occuring at one specific point of our process. It is at the cut to length operation. It has came to light due to a customer complaint. We can see what we believe is causing the problem,but have not been able to see a clear solution at this point.