The procedure is detailed in your owners manual and in many places under "FSS Reset"
Here's a link to one:
http://www.peachparts.com/shopforum/showthread.php?t=108414&highlight=fss+reset
For yours I believe it is:
Stage 2 Basic Flexible Service Systems 1998
Stage 3 Advance Flexible Service Systems 1998
Engines: M-111 (4cyl) M112 (V-6) M113 (V-8) 104 (6cyl Twin cam) 119 (V-8) 120 (12 cyl) 606 (Diesel)
1 Turn electronic key in the steering lock position 2
2 Within 4 seconds, press button "O" twice
3 Note! The present status for days or distance is displayed.
Within 10 seconds, turn electronic key in steering lock to position 0
4 Press and hold down "O", while turning electronic key in steering lock to position 2. The present status for days or distances is displayed once more. Keep holding down button"O"
Note! After approx. 12 seconds a signal beep sounds and the display will show 10,000 miles or 15 000 km for other countries
5 Release button "O"