how do I close a thread I started?

There may be an option in/under Advanced...If it is possible, you would need to instigate it from the first post in the thread you started.
Try clicking "edit" within the post and then click "additional options"
I had done this once long ago as i somehow started two threads with the same topic...kind of like a repeat post and did not realize till after.
DJI may have removed the ability though for the OP to do this, not sure though

EDIT....I just tried it and here is what i found,
It worked to delte the thread if it was created and there were no reply's
however, if someone had replied i could not delte the thread....

You may need to have DJI do this for you....

thanks northofthe49th