A lot of my answer will be gross simplification and please take it with a grain of salt. There are notable counterexamples here.
So the closest thing to harmonization in a raga is a concept called melharmony. https://en.wikipedia.org/wiki/Melharmony
An extremely simple example of melharmony (and this is a really special case), you could just play thirds from a given note (much like how you harmonize a major scale, Shankarabaranam in carnatic and the bilawal thaat in hindustani) while you play the melody.
The important thing to understand about melharmony is that unlike most of western harmony (where harmony dictates a framework on which melodies are played like say bebop improvisation), melharmony inverts the role (the melody is the driving force and the harmonization is an enrichment, similar to how chord melodies are constructed in jazz).
While counterpoint is possible, its was not the original intent of melharmony and was later added in by Western Composers (notably Robert Morris).
Its important to note that melharmony is avant garde music. In the more classical traditional sense, harmony (at least harmonic motion) is non existent in both forms of Indian classical music.
There are more adhoc treatments of harmony. For instance if you play on a raga from the Bilawal thaat (aka the major scale) or the Asavari thaat (aka the minor scale) all the theory of functional harmony should be accessible.