how do i close a thread which i posted
You can only pm a moderator (or hit "report" in the thread) and ask that they close it. They may or may not do so.
We do not close threads on demand. All threads you open will usually remain open. Threads are normally closed only when they don't meet the guidelines or they run out of hand.
So please don't report threads asking them to be closed.
As stated in the PF Rules:
This applies to requests for threads to be closed.
Separate names with a comma.