Reduce spiciness of chili
To some extent chilli (capsaicin) is like salt in that the best way to reduce the taste is dilution. However with capsaicin you can also make use of the fact that it dissolves in fats. But you can't neutralise it - up you'll always be increasing the size of the dish. 

To dilute you could make another batch without the heat, and combine the two.

A good source of fats is dairy, so you can indeed stir in sour cream (this isn't a time for the low fat version) or cheese. Both of these are often served with chilli, and take some of the heat away even then, but you need to mix the in. I use cocoa powder in my chilli, others use dark chocolate, which is easier to add at the end. Again, this is a source of useful fats, but be sure to get one with a high cocoa content unless you like your savoury food sweet. With all of these it's a good idea to cook a little longer, so you can also add a bit more of some of the other ingredients - beans, tomato, the liquid in your sauce (perhaps thickened with a little cornflour), etc. which will dilute the heat. You may be left with a portion for another day.