When you key on the car and the time for service message is displayed. Press and hold the "clear" button on the SID for about 8 seconds. It's a little different then resetting your milage or other functions since as soon as you touch the clear button the message disappears (but it's not reset and will come on at next key on). You should hear a "chime" and next time you start your car it should be gone. It takes 3-4 tries on mine, so keep trying if it doesn't work the first time........ If you have an owners manual it should be covered under SID "Check Messages" section. Page 19 in mine.
You have to push the clear button until it beeps twice then it will clear. If it beeps only once, it'll clear the message until you turn the car off but won't be gone from the memory so when you retart the car the message will display again.