There is not easy answer to this without knowing more about the spoon and how it was used. Stainless turns blue for a couple of reasons:
-- the stainless was used at too high temperatures which affects the coating of many versions of stainless. The 18-10 metal is less susceptible to this than others
-- stainless used more for serving and table use are coated and this coating can react with some foods. This can frequently be remedied with Bartender Friend or baking powder.
Without more information, I am not sure what would be the approach to "fixing" the blue tint on your spoon or even if it is fixable.