This forum doesn't have the option for us to delete the topic or post, but we can modify that post and can write there nothing and can leave that space empty this will indicate that the post is useless and thus after doing this we can report it to the moderators and can ask them to delete the post for you. If the moderators are given the access to do that, otherwise only the admin can do that. I also once mistakenly posted in the same thread tow times.
And I had to delete the post, and that's when I realized this forum doesn't have any delete option. So, I prefer you to delete the post by editing the post and enter the text there as Delete this post, if any moderators saw this, This might solve your problem, or we should just ask admin to add this feature.