You should solve the issue that caused the warning first or you may be in for trouble down the road. You can pull the codes at most auto parts stores or a mechanic can do it for you.
That being said, if you pull the battery and turn the key to ON to discharge the power that should reset the light. If it returns immediately then you still have a problem.
Also see:
How_do_you_reset_the_Maintenance_Required_lamp_in_a_1994_Mitsubishi_Montero
After my 1995 Montero turned 150,000 miles the
I changed the battery and voila' - no more light.
maintenance with engine
The maintenance light,You will need to take it to a Dodge dealer to reset it. Or get a DBR-2 code scanner.BIG $$$
aperantly take the light out
The maintenance required light requires a scan tool to be reset.
How do you reset the maintenance required light in the 2011Toyota RAV4 with a smart key starting system
To reset the maintenance required warning light on a 1989 Dodge Dakota, unhook the battery connector cables for 10 minutes. Reconnect them and start the vehicle.
With the engine and ignition off push and hold in the odometer reset button. While holding that button in, turn on the ignition but do not start the engine. After about 5 seconds the light will go off and the maintenance required light will have been reset.
How do you reset the maintenance light on a 2001 Honda accord ex I found some options at http://www.tegger.com/hondafaq/maintenance-reqd-light.html#why
Read your owner's manual.
disconnect the battery