white balancing has only the super basic rgb sliders interface (no temperature/CCT+tint so far, i might ship that at some point). there are, however, a couple of presets. if you press ctrl-p in darkroom mode, it’ll bring up the preset menu. if you type neutral into the filter field, the pick-neutral.pst is the only match (if you don’t have custom presets). apply this to place a colour picker module in the graph to conspire with the colour module. this can be configured to do deflickering, but this preset uses it to pick a neutral spot for white balancing. initially, the preset covers a large spot centered on the image. if you navigate to the pick:01 module you can pick another spot. this will be moved to neutral/white.
there is another set of presets, colour-monk-[0-9].pst (type monk into the filter field). these use googles skin tone scale as reference colours instead of neutral. with a bit of luck you can use them to white balance for skin tones (picking a skin patch instead of a neutral patch).