how do I turn on the interior lights of a 2017 buick lacrosse

Look into the owners manual.

Should be a setting to change when the interior lights come on. As Rowefast posted, that info should be in the owner's manual or better yet, take it by the dealership and have them show you how to do it.

There are two buttons up top by the map lights. One says OFF with a picture of the car with the doors open. With the ignition on, press that button so the little light goes off. The other button will turn all the interior lights on/off.

There is a little switch on the left side of the steering wheel that adjust the interior lights. Push it up or down for the dimnest you preferred.