Do you have the Medallion Spartan Instrumentation Operators Guide as it pertains to your coach? If not, I have attached the one that was published in 2004 (Rev A) and I'm assuming that it will pertain to your situation. Instructions on how to set the trip odometers are on page 10.
You should have two trip meters. One, Tripmeter 1, can be set by either the reset switch on your instrument panel or through the Medallion Info Center. The second one, Tripmeter 2, can only be reset through the Info Center.
To reset trip meters through the Info Center, navigate to "Trip Center" by using the "up" or "down" keys above and below the "enter key" ("E").
Once you are in the "Trip Center" mode, press the "E" key. Then use the up or down arrows to navigate to the "Trip Meter" mode. Then press the "E" key. Use the "toggle" key or "T" which is the first button on the left side to navigate to either "Trip Meter 1" or "Trip Meter 2"
Once you are in the "Trip Meter" 1 or 2 mode, use the "E" key to reset the odometer back to zero.
It will probably be easier for you to use the flow chart on Page 10 of the manual than to follow my poorly written instructions, lol.
Good luck with it. After doing it the first time, subsequent resettings should be very quick and intuitive.