How to turn off engen light in 1998 opel corsa lite

You don't just want to turn it off until you determine why it came on! Your question indicates you have checked nothing out;you just want to turn it off and that solves nothing. Start by checking your gas cap.

Just disconnect the battery for a minute that will turn the light off until the computer reboots and the problem sets the light off again. That's what the light is for to tell you there is a problem.

and disconnecting the battery fixes nothing. You have to find out WHY it went off. Could be something not so bad to somthing that could end up costing more to fix later rather than addressing it now. AT LEAST CHECK IT OUT before you just turn it off.