How do you reset a service engine soon lignt on a Altma 2005?

Have you taken your car in to see why that light is on? When they find out why, the light will go off. It could be something little, like a pollution problem with your gas cap not screwed on tight enough.

In my Subaru outback it was just such a problem. I had gone without a gas cap and that was enough for the 'service engine soon' light to come on. Once the mechanic had gone through all possibilities, the computer told him what it was.

Get it check out, it could be big trouble or something small.

If the tank has recently been filled, a loose fill cap could be the problem.
But with emissions being so closely scrutinized, there are common software and parts updates. Have the stored codes read and annotated, and then contact your manufacturer to find if they have a recent update. Let us know here what codes they found!!
If not, post the code here and "we" may have more input...