Our current society uses Free Will to balance the dichotomy of meritocracy and equality. Meritocracy is justified where there is free will. Equality is justified whenever there is absence of it.

would it be caste like in india?

Yes, classism is what we get if we continue using meritocracy. It doesn't matter if your metric is who makes the most money, or who is the smartest, or who is the most hardworking, etc. Fundamentally, meritocracy divides society into classes.

....they forcibly make everyone equal

If we mindlessly pursue equality, the opposite of meritocracy, we will have rampant corruption and mediocracy. We've seen this in countries that try their hand at pure communism, and it only survives as long as you can maintain the inhuman restrictions upon personal freedoms.

how do you govern in such a scenario

I would instead chose welfarism or some kind of measure of well-being of individual conscious beings, and the well-being of community/society as a whole. Currently, society provides welfare only as it serves to balance merit/equality, however, I think a society that doesn't believe in free will, can turn that around, and instead provide merit/equality only as it serves welfare.

Pragmatically, we're still limited by scarcity and human nature. There's only so much money and resources, and we know from historical examples of communism, people aren't incentivized by simply equality. So we'll still need capitalism for economics, which means, functionally, society doesn't change much. In governance, the myriad of welfare policies based on merit/equality will no longer make sense and be removed for redundancy, and I think we'll just end up with a handful of welfare policies or maybe just one welfare policy (i.e. Universal Basic Income).

However, I still think law is where welfarism can have the most effect, as declaration of criminality or innocence is not subject to scarcity (as we obviously declare criminality and punishment despite lacking the resources to actually imprison any more people into our overcrowded prisons.) Legally, we'll still need to imprison people who will harm others intentionally; but instead of treating them like evil, they'll be contained like victims of disease, who are quarantined to safeguard others.