@Tatjana13
I'm afraid that you cannot change a review after it's published, only ask for it to be removed. If your review just said 'I will contact you when we arrive in Belgrade,' then the host could even ask for it to be removed, on the grounds that it is not relevant to the listing.
However, if you left the host a 5 star rating, it would not be in his/her interest to have the review removed as the rating would be removed too.
I would just message the host apologising that your private feedback got posted by mistake. I am sure they wouldn't mind because you left 5 stars and that is still better than no stars!