He did nothing, He believed that it was part of a"boom - bust' cycle of capitalism. He therefore believed that the economy in general, and the stock market in particular, would in effect fix themselves. read more
He believed the government should not go in debt no matter what. This limited what he was willing to do. Please note that economists back then agreed with this idea so it's not like Hoover was just being mean. In fact, FDR believed the same thing and it's often said that he undermined the New Deal by trying to balance the budget too soon. read more