I am glad you have two good working headlights now.
Water in the headlights is caused by either broken glass or bad seal. To replace them, you have to remove the side marker light. Open the hood, there is a Phillips screw holding the side marker. You will see a small light-gray lip coming out of top of the marker. Remove the screw and pry the marker out to the side of the car. Once the markers are removed, you will see two 10-mm head screw that hold the headlight on the side; there is another 10-mm nut holding the headlight on the back; and there is another 10-mm head screw holding the headlight on top. That will remove the headlight. There is no need to remove any parts of the front bumper cover like other cars.
If the front surface of your headlights are too damaged and not clear at all, you can consider buying new cheap aftermarket headlights. You can find them as low as US$100 each.
For the black retainers, they are Nissan 26029-7B000. You can find them in eBay or internet, perhaps AZ has them too.
Many years ago, I bought a new pair of headlights and retrofit them with HID bi-xenon 2.5″ FX-R projectors. The whole retrofit cost me around US$600. I did the installation myself but it requires some skill with the dremel. However, the final result was outstanding modern HID projectors exactly as you see in any infinity today.