Usually, RV water heaters are not adjustable. Attwood makes an adjustable thermostat you can buy and install. I don't believe Suburban does. If your heater is heating the water, but not hot enough, you will probably have to replace the thermostat switch. They are easy to replace and can be purchased from Amazon cheaper than most places. However, before you do that, check your bypass valves on the heater. The one that bypasses the heater could be partially open and you would be getting a mix of hot and cold water. If you have a temperature probe, the water should be about 140 degrees F.
BTW, Google is your friend! You will find all sort of info there including how to videos.