The Nikon D90 is not designed for video streaming.
I found a software product that claims to be able to handle it; see http://sparkosoft.com/how-to-use-dslr-as-webcam . I have no information on how well it works.
Other than that, the solutions I find documented involve using the HDMI output, which works at the same resolution as the LCD display. One product specifically designed for such a use is http://www.dvestore.com/blog/review-of-the-livestream-broadcaster-with-nikon-d800/
The D90 is not compatible with either of the Nikon wireless remote accessories, the WU-1A or WU-1B; see http://imaging.nikon.com/lineup/acil/accessories/wu-1b/ and notice that those specifically say that you cannot use them for movies (only for stills)
Some of the newer Nikon cameras offer built-in Bluetooth sharing using what Nikon refers to as "Snapbridge"; see https://www.nikonusa.com/en/nikon-products/snapbridge-app.page#connected-cameras. That appears to offer remote control better than the WU-1A/WU-1B but it is not clear to me that it supports video streaming.
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Side note: for information about using Cannon or Sony cameras for live streaming see https://www.mathworks.com/matlabcentral/answers/276636-image-acquisition-toolbox-supported-dslr-cameras#answer_216019
