I'm not sure what you mean by linking the thread to the forum. Do you mean you want to post your hub's URL into the "weekly topic" forum thread? If so:
Go to your hub. At the very top of the window is a web address box, with some text in it that starts "geetbhim.hubpages.com/hub/..." Highlight the whole text and copy (Control+c or Command+c). Go to the forum thread and in the comment box, paste your text (Control+v or Command+v) into a reply box.
Do you mean the reverse? That you want to link the forum thread to your hub? Just follow the above instructions in reverse.