Select your object. Go into Edit Mode. Select everything. Press P and choose By Loose Parts.
You will see that your model is made up of five separate meshes, and that would be problematic to print.
Two of these meshes seem to be floating around and not part of anything; it seems save to delete them.
The other two are cubes in the dashboard area. If you need them, i think you need to manually make hem part of the main mesh by deleting geometry around the cubes and connect the cubes to the rest using F. You'll want to be carefully not to create non-manifold geometry while doing this. For example, when you are done each cube should have 5 faces, and not 6 where one face is hidden on the inside.
This might also help:
What is non-manifold geometry?
I'm not sure but I suspect you might run into more problems trying to print this model, but i guess you can start by solving this issue. In any case, good luck.
As I suspected your model had a lot of issues that need to be resolved before it can be 3D printed. I've looked a bit closer and for instance, next to the gear stick there are a lot of faces stinking into the floor. It makes me wonder how this model was created, and if it were possible to resolve these issues at that first step.
In any case, Select Non Manifold might help if you want to visualize and learn about the issues of this model, or any other model for that mater.