Our language is conceptual

, hence the concept of "you changing your beliefs" doesn't mean that you literally reach down inside your brain and insert some beliefs, and you throw other in trash can.
What constitutes "you" is not a single entity, although it may seem like it. There are a number of compartmentalized brain activities that you have zero control or even awareness of. Many of these are responsible of processing information and informing your conscious choices.
Hence we may form false beliefs without ever knowing precisely because our subconscious or even conscious parts of the brain know the difference between reality and imaginary models.
That's why we developed methodology that keeps these issues at bay, and we generally self-evaluate and fact check. Sometimes the facts can be intentionally hidden from us, like in religious setting where dialogues that debate against any given belief system are suppressed and discouraged. Thus, there's only one-way flow of facts and information that prohibit rational choices.
When we say "only you can change your beliefs", we mean that only you can either consciously deny honest evaluation of facts, or you can allow it and take it on as a model.
Earlier I've asked you whether you believe that you can be wrong about God. You said that you can't be... hence it's an outright denial about any conflicting evidence... because you can't possibly be wrong. It's not a choice to believe something. It's a choice of closing your eyes and ears and saying "lalalalalal" by quoting the Bible.