The DR900S is designed to work up to 167 degree F. You do not have to worry about the temperature affecting the dashcam, because when it reaches the high temperature cut-off, It will automatically shut down to prevent damage to the camera.
There are known common factors that may cause the dashcam to overheat like continuous Wi-Fi usage,parking the car under direct sunlight with camera on for long hours etc.
If you are constantly using and turning the camera on then we suggest you to try to cool down the surrounding environment allowing some air in car to balance the heat emitted from the device. Right ventilation is necessary to keep it from absorbing too much heat that may also come from the surface near where it is installed.
Also, if possible, make sure that your dashcam, is not directly parked in the sunlight. If there is no shade available, you might want to change the position of your car to not get a direct sunlight exposure.