The air filter on a Buick LeSabre (depending on the year, as the location might vary slightly) is typically located in a plastic housing
under the hood, near the passenger-side (right) of the engine. It's often a rectangular black plastic box. You'll likely see a large hose connected to it.
To be absolutely certain, check your owner's manual. It will have a diagram showing the exact location and instructions for changing the filter.
