Hand tools are of thick metal to allow a good leverage to be aplied. They are small and have tapered edges to get into these areas with difficult access. You can get them in different lenghts and angles to allow you to get to a different positon to get into the inner edges of those panels.
If you can't get in through the top by their access from the window, there are normally small drainage holes that allow the rainwater to run out. The small access holes for these tools are around a lot of panels, in doors especially on the lower edges. These useful litte hand tools can get in those tiny drainage holes and then you can still leverage out the dent from the inside.
