The easiest way is to hit the "alert" button (exclamation point inside a triangle in the upper right corner of any post) on a post in the thread. The alert function will let you write the mods a quick note about why you're alerting--in this case, with a request to move the thread from z forum to y forum.
Or you can send me a PM.
We can merge multiple threads into one, but it's usually better to wait for the thread to be moved. When threads are merged, sometimes the order of the posts coming from multiple threads can be a little confusing for readers to follow.