Need to reset computer on 05 Lacrosse I don't have a scanner

Without a scan tool or a code reader you'll have to wait for the computer to run the diagnostics and determine that the problem that triggered the check engine light is fixed. You can speed up this process by keeping your gas tank between three quarters and one quarter full. The computer will not run the diagnostics on certain systems if the gas gauge is above or below those parameters. Disconnecting the battery will not reset it either! Hope that helps! Jim

Your local auto parts store can reset the light for you but it will come back on if you don't fix the problem that caused it to illuminate.