Describe where the water first leaves its normal route.
If you have watched overflow from a safe indoor or ground-level position, identify the corner, edge or outlet involved. Explain whether the concern appears during ordinary rain or only a heavy downpour. Leaves, twigs and other collected material can reduce flow, but the observation does not prove the entire rear gutter is blocked.
Mention a pipe that seems disconnected or a joint that drips. Cleaning can remove suitable debris; a broken connection needs a different decision. Existing photographs are enough for the initial discussion, even if they do not show inside the gutter.