What does 其 mean in 授予其创意改变世界和影响今天所有人类的人?
其 means 他/她的 (his/her), it modifies 创意, so 其创意 means "his/her 创意".

The structure of the whole sentence is V+O, i.e. 授予(verb) + 人(object). "其创意改变世界和影响今天所有人类的" is a long modifier which modifies "人". The museum award the prize to "people", what kind of people they are? The people "whose 创意改变世界和影响今天所有人类".