Have you taken it back to the hobby shop?

I assume you are an experienced flyer, but just in case you are not, when you push the stick forward, away from you the elevator should go down.

Since this is an RTF plane that is all set up at the factory, if it is not working properly you should send it back or return it to the local hobby store.

Have you called the Horizon Hobby support line? Number is on the manual. You did read the manual, right?