Sometimes after editing a blogger post the URL for the blog post might end up like _02.html. So to edit the url, there are two ways. If you don't have any comments, then you can create another post with the desired title, so that the url follows the title, and paste the contents of the post. Then you can schedule the post to be somewhere near the original post's date and time, and then publish the new post. After that you can delete the old post.

If you seriously messed up the urls, then export the blog and its template. Then rename the current blog to a random address, and create a new blog with the original blog's address. Import the posts and template to the newly created blog and delete the old blog.