You can delete your post by going to your profile (see here how to go to your profile) and clicking on the ‘Posts’ tab. Here you will see an overview of all the posts you have posted in the Community Wall. Click on the 3 dots in the top right corner of the post to delete your post.
See below where to find the ‘posts’ on different devices.
Desktop & Mobile
You can find the ‘posts’ tab above your profile photo.
App
You can find the ‘posts’ tab below your profile photo.