how can lock this ?

Q: How do I delete/lock my own thread(s) when I no longer need them?
A: On the top right of your post is a delete button. You can delete threads if nobody has seen them. Otherwise, just click "Lock topic" link at the bottom left.

Q: Can I enable self-moderation on an already existing thread?
A: No. Just lock the old thread and start a new one with self-moderation enabled in "Additional Options...".