The Over-range indicator in the viewfinder is not the cause of overexposure, it merely indicates that you're about to overexpose and corrective action should be taken.
The automatic exposure control on the X-370 is aperture-priority. This means that the user sets the lens aperture, and the camera adjusts the shutter speed for correct exposure. However, one should keep in mind that the effective range of this automatic adjustment is limited. If the scene is too bright, the limit is the fastest shutter speed the camera can achieve (1/1000), if the scene is too dark, the limit is the lowest shutter speed you can use without risking visible camera shake (1/60 or 1/30, 1/15 if you're brave).
The bottom line is, if you see the Over-range indicator in the viewfinder, you should stop down the lens aperture until the indicator goes out. This is done by rotating the aperture ring on the lens barrel, which is the ring closest to the camera body, marked with numbers 1.7 - 2.8 - 4 - 5.6 - 8 - 11 - 16 -22. Brighter scenes require higher numbers.
Conversely, if you see that the camera is selecting a slow shutter speed (1/30 or slower) you should set a larger lens aperture (smaller number) to avoid visible camera shake.
The recommended setting depends on the type of film you have in your camera and the lighting conditions.
If you're using a moderately fast film (400 ASA) outdoors, you should set the aperture in the range 16 (sunny) to 8 (overcast). For a moderately slow film (100 ASA) you should set it from 8 (sunny) to 4 (overcast).