You 100% flip BOTH switches on.
The bloom mode in led lights activates colour diodes near the red side of the spectrum.
This is what the plants need in bloom because it activates specific chromoproteins in the cells responsible for bud growth.
At the same time, the VEG switch emmits blue light responsible for establishing a biorythm in photosynthesis and overall growth.
So yeah, switch them both on.
Usually led lights come with a manual that tells you what to do in every stage.
Nice and happy plant by the way.