Looks like the same gauge on my Gen 4, the lower button allows you to choose your settings, scroll down to settings on your gauge hold the button down for like 2-3 seconds and you should be able to change your indications to RPM/MPH.
For some dumb reason you have to keep the speed on the screen. If you scroll with the bottom button till the word speed comes up and stop scrolling that gets you RPM on the Center and then speed on the bottom. I’ve been trying to get RPM in the Center and engine temp on the bottom but there’s no way. I couldn’t care less how fast I’m going. As long as my RPM is consistent I can judge track speed by how I’m moving through the snow.
I like to watch temperature on trails in and out. Use the bottom button to scroll until eng temp displays but everytime reverse is used it goes back to settings. What am I doing wrong.