Have him go to www.annualcreditreport.com and go through all three credit bureaus and dispute the charge.
If the creditor does not answer in 30 days, it will be removed. They usually do not have anyone assigned to do this at small companies.
It will take some time, but it's the only way to do it and it is free! That website is provided by the 3 credit bureaus by the government so that all Americans can check their credit once a year.
Do NOT go to a credit cleaner-upper. This is a small thing to get done and he does not have to pay money to do it.