What does the robot really want? Literally money? Power over people? Just the planet itself, with humans as nuisance?

In any case, break in to a modern biotechnology lab with everything needed for genetic engineering. Create a highly infective biological thing (not necessarily a virus) that, after infection, creates a biological circuitry that makes a human perfectly obedient after some defined signal. A much simpler versions of that already exist [0]. Now just start infecting people and use their resources to spread it even wider. Even if a small part of a population is immune it's not a problem.

Few days at most and you own everything.

[0] https://en.wikipedia.org/wiki/Behavior-altering_parasites_an...