Wear a mask. Wear a particle mask to prevent inhaling the spores. Look for moisture in the location and get that eliminated; clean the files of a much of the mold as possible. When the moisture is resolved infusing thieves brand essential oil into the air (which may be uncomfortable to humans) will help to kill any remaining mold spores. If you can't get cooperation may need to look for a new job location.
Remove &remediate. Unless you are allergic to mold, there is no immediate danger. The moldy files should be replaced with new ones. To prevent mold growth, have an expert check the hvac system, keep humidity low, etc. Prevention is the best treatment.