Note when the patch first appeared, when it was treated and when you noticed it again. Photographs taken on different dates can be useful, particularly if the area changes between wet and dry periods. Explain products or work already tried, including any repair that happened nearby. Give an overall room view as well as the surface detail without disturbing affected material. A timeline helps describe the problem without deciding its cause in advance.
Other household dirt can be discussed through a one-off home clean. Returning mould needs its own assessment and treatment request rather than another general cleaning task.