Blog index page link name

I found this weird issue: my blog index page was linked to the home page, when I clicked blog on my website, it took you to the homepage. It was ok earlier, and I did not change the link. I don’t know why the link changed to homepage itself. You can see in blog page under dashboard, the permalink became xxx.com, and the /blog was missing. But it does not allow you to edit the permalink, it is NOT editable. Only this page’s permalink is not editable because you can NOT find edit button displayed by permalink. Other pages in dashboard are fine.

So I created a new blog index page, and trashed the old one. Now when you click blog on the website, it can link to the blog page content, but the link displayed is xxx.com/blog-2 now. I tried to change it back to /blog, but never sucessful (although it allowed me to edit it to /blog in dashboard, but it will always go back to /blog-2 itself once you publish. I wonder how I can get my blog index page named .com/blog again? Many thanks!