i need to  know how to make the icing smooth on a cross cake top

please tell me how to make icing smooth on a cross cake

An easy way to do it is either take a clean paper towel or piece of clean cotton material and let the icing dry just a bit, then lay the paper towel or material over the icing and gently rub back and forth with gentle pressure and do that until you've done it over the entire cake and then carefully lift it away and it should be pretty smooth. Be careful when lifting the material or paper towel away to make sure that icing didn't stick to it. Make sure your icing is not sticky. Good luck! 

@purple305   Don't know your level of expertise, but the easiest way on a curved surface like that is to use fresh buttercream that has not crusted yet, then use the techniques shown on this youtube video by Olga Zaytseva:  How to make a frosting smoother

good grief.... tried to send links and info and CC wiped out most of my post.   

Make sure the homemade frosting smoother is STRAIGHT.

Look up cross cakes on CakeCentral for ideas.