bbPress works fine, but

when I tested writing topic with a Participant account, I can delete my own topic

how can I fix the problem?

[@anonymized-5853594 Inactive 11 years, 9 months ago]

Your topic title and stated problem contradict each other. Could you please clarify what the exact problem is?

[@greenartweb Participant 11 years, 9 months ago]

I made a ID which is a Participant account. When I tried to delete the content after I posted a content in Topics, I couldn’t find trash or delete button.

cannot Participant account users delete their own topics?

[@anonymized-5853594 Inactive 11 years, 9 months ago]

No, they cannot. Only Moderators and Keymasters can.
You can find which types of users can do what in the codex, it has an article about user roles and capabilities.

If you like to change what users can do, you would have to look for a plugin with controls what users can and cannot do.