[veenuisthebest]

you usually merge threads manually when they have almost the similar content/posts.

To do this:-
1. Select the threads/topics you want to merge.
2. From the Moderation drop down-> select Merge Threads-> Go
3. It then asks to select the destination thread from the two.

You can even merge similar posts from within the specific Thread's Moderation dropdown.

I hope this is what you are looking for !!