Move the detached poly out from the mirror and then chamfer the green edges on the mirror box.
On the back, scale down the poly to the size shown and move it outwards a little to make a slope.
Make the extrusions shown in the picture. Chamfer the edges shown in light blue.
Getting back to the poly you detached earlier, this will become the actual reflective glass of the mirror. All you have to do is extrude it's edges a little way inwards as shown and chamfer the green edges. You can then place it back inside the mirror. Position the mirror on the bar that we made earlier and rotate it a little like a real mirror would be.
There's a little handle that is located on the passenger side of the dashboard. I think by now, something like this should be no problem for you so I will just tell you what I did and let you do it by yourself. Basically, start with a spline and make it renderable then convert it to an editable poly and scale edge loops to get the bulges at either end. Simple!