Chris Feichtner (nocamerabag on Instagram) has a good explanation of using the noise reduction tools in Lightroom Mobile on his blog. In particular, he notes what all the different sliders (like Detail and Smoothing) do, not just the chroma and luminance sliders.
Tutorial: How to use Noise Reduction in Lightroom Mobile
An easy to follow tutorial about how to use Lightroom Mobile to apply noise reduction to your photos on iPhone and iPad
nocamerabag.com