Start with a screenshot describing what you want done to the window. If the model is too big to attached to this forum, try uploading to google drive or dropbox and post the link here.
It’s a bit of a process. I’d recommend making sure you’re well versed in SketchUp basics before attempting something like this. Check our learning videos here: https://learn.sketchup.com/
It’s one of many ways to look at attempting it:
bring your image into SU and scale it. Move and rotate either image or car so they are aligned.
Then turn on hidden geometry in order to ‘patch’ the existing window that you’ll be updating with the new design. Use Sandbox Tools ‘From Contours’ here to create new surface.
You now have the outline of the new design embedded into the new surface. You can use extensions like 'Joint Push Pull’ to extrude the window cutouts inward. This is tricky as you can see there is also a slope along two sides so it’s not just a straight push. An offset and then sandbox from contours is likely required show that transition from glass up to outer surface.