In summary, you can delete a topic that you have already posted on most online forums and discussion boards. The process for deleting a posted topic may vary, but it is usually done by clicking on the post and finding a "delete" or "remove" button. Deleting a topic will typically also delete any associated comments or replies, though this may depend on the specific platform. If you have accidentally deleted a topic, you may be able to undelete it depending on the platform's features. Some forums may have a time limit for deleting posted topics, so it is best to check the guidelines or rules beforehand.
After posting you have a 700 minute window to edit or delete, after that it is fixed. You can report the thread and explain why you want it deleted but it won't necessarily be done.