How to kill a lizard. It is in my house and I can not find it

At this point I wouldn't worry about it. The reason is it will either die on its own from lack of food or return to the outside. Unless it is a harmful kind then there is no reson to intentionally kill it.

In some places like Hawaii it is considered good luck to have one in the house.

Have you considered luring it into a humane trap and releasing it away from your house?