How to reset the change engine oil soon light on Buick 2000 LeSabre?

Turn the ignition to accessory on. Pump the accelerator three times. The Oil Life Monitor will flash for about 5 seconds indicating it has been reset correctly.
The oil life monitor is a function of the Powertrain Control Module (PCM) that tracks operating temperature and engine revolutions per minute (rpm). Obviously since the light came on again the temperature is too high for the engine rpm. The incorrect oil weight or type could have been used and you need to change it with the correct weight and type. The other possibility is that a sensor or the PCM has a problem and you will need to have an OBDII code scanner to identify the problem. That will cost you around $70.00 if the mechanic knows what he is doing he can tell you the problem. I think changing the oil with the recommend weight and type again would be the cheaper route.

SAE 10W-30 is best for your vehicle. However, you can use SAE 5W-30 if it’s going to be colder than 60 F (16 C) before your next oil
change. When it’s very cold, you should use SAE
5W-30. These numbers on an oil container show its
viscosity, or thickness. Do not use other viscosity oils,
such as SAE 20W-50.

Try This method used for cars with a Driver Information Center (DIC);
After changing the engine oil, the Oil Life System
should be reset. It will not reset itself. To reset the Oil
Life System, press and hold the RESET button on the
Driver Information Center (DIC) for more than five seconds while OIL LIFE INDEX is being displayed. The oil life will change to 100%. The Reset button on the DIC control panel is located to the left
of the steering column.