How do i close a thread?

Only the room mod for the room where the thread is located, or a super mod, or an admin can close a thread. There are very specific reasons for closing a thread and a thread that continues to provide good information (and hasn't become problematic) will remain open. Best suggestion I have is to PM the room mod regarding the thread in question and if they concur with your reason for requesting the close of a thread you have opened, they'll be happy to accommodate.