Calling is the quickest route. Say what you see or smell, which room, how long it has been going on, and whether there is a known leak or storm damage, and the crew sets a time to come and look. For a visible patch with an obvious cause you get a written scope from that visit; for hidden or spreading growth the crew books an independent assessment first.
If a call is not convenient, send the form with your neighborhood and a line or two about the problem, and you get a call back the same day. A photo of the growth helps; a photo of the whole wall or ceiling helps more, and so does a note about when the AC was last serviced.
For water actively coming in, a burst pipe or a flooded room, call rather than write. Drying calls are returned first, because the two-day window is what keeps a water problem from becoming a mold problem.