Need to change the water filter on my Sub Zero

Hello. The factory indicates your unit required an in-line water filter if your plans were to use one, or the installers added it. There was no indication of an internal filter in the fridge itself. If there was it should be easy to see or find. However this can be good news for you also as your filter (if installed) migt be easy to find and access behind or near the fridge if installed well and a good quality but common form of water filter you can easily replace may have been used, if installed. Otherwise if you have whole-house water filtering already they may not have added any further filtering.

If you can contact who installed your 690 they should be able to tell you where they installed it and what type. If not just have someone follow your water line to the fridge unit, and see what turns up as you make your way along to the place where water connects to the fridge.
http://www.subzero.com/resources/products/downloads/600installguide.pdf