In order to plot anything on siteviewer, you need to use the propagationData data type or similar object. This means you minimally need the coordinates and value to plot, stored as an array list of sorts; minimum is location coordinates. Some example code is below:
siteviewer("Position",[10 10 1910 1080]);%creates the siteviewer instance
plot(pd, "LegendTitle", legendTitle, "Colormap", flip(decimap), "ColorLimits",[-150 0]);%plots the data on siteviewer using 2D markers
Where pd is a propagationData data set that contains lat/long/value (or X/Y/Value), legendTitle is the title of the scale, decimap is the color scale in decimal format, and colorLimits are the scale limits of your propagationData. propagationData does not need to have RF values, but must include lat and long.
Its also possible to map a 2D result onto a 3D geotiff plot using axis and surf, but that's outside of this questions focus.