Issue: For some reason The Page Title Name showing the name First blog post title instead of the Page title ie 'Blog'.
I have created a Page with the title name 'Blog' and assigned it to a template with the option Other -> Blog Posts Index.
And assigned this page to WordPress Settings -> Reading -> Post Page = Blog.
> For some reason The Page Title Name showing the name First blog post title
It sounds as though you've used Insert Data > Title, which will retrieve post titles only (this is most likely why you're seeing the title of the first post). Please try using Insert Data > Archive Title instead.
If you find that shows "Archive: Blog" or something similar, you can add the following code to the Code Snippets plugin to remove the text "Archive: ":
The Blog Archive page's template is Inherited from the Main Template ( In main template the Data-Insert is Title). I cannot change that to Archive template it will mess up the title of all the pages on the website.