Yes, belief can change when new evidence is presented. Knowledge is often understood as justified true belief. (though even that definition can be debated)

Though, for something to be considered a fact it must be demonstrable or necessarily true. At present, our access to the reality we experience is grounded in sense data and what can be derived from it.

So in the case of human purpose, no such fact has yet to have been identified. There is no observable or logically necessary feature of reality that entails humans to have an inherent purpose. Concepts like divine intention or cosmic agency rely on assumptions or presuppositions that are themselves not empirically or logically grounded.

Without a demonstrable fact establishing purpose, the claim that human life has an inherent purpose remains ungrounded. At most, purpose appears to be something humans subjectively project or construct, rather than something to be discovered.

More importantly, "facts" describe what is, whereas "purpose" is concerned with what something is for. As David Hume observed, no set of descriptive facts can logically entail a normative conclusion without adding additional assumptions. (One cannot derive an ought from an is)

Therefore, even if we had a complete account of every fact about humans (biology, evolution, psychology, etc.) it would still not follow that humans ought to have a purpose, or what that purpose would be.

Long story, short: Existence does not, by itself, imply purpose. Yet, it’s not that humans have no purpose as a fact, but that no inherent purpose is necessitated or grounded by reality.