Looking at the video of your rig the HWH should have a panel that can be removed with 4 screws just below the pantry cabinet (left of fridge). The bypass normally consists of 3 valves. Hot water, cold water shut-off and the bypass T'd of between the two. This bypass valve can be used to somewhat temper the hot water to help prevent scalding yourself in the shower. It isn't as good as an auto tempering valve, but it can help by cracking the valve open, allowing cold water to mix with the hot.