I want to have custom template for my blog post and also for portfolio. currently there are no page attributes (Parent and template) in the blog post page.
Hi There,
Please take a look at this article: http://www.wpbeginner.com/wp-themes/create-custom-single-post-templates-for-specific-posts-or-sections-in-wordpress/.
Hope it helps 
i have tried but unable to customize
Hi there,
Customizing the custom page you have create unfortunately falls beyond the scope of our support. As such, you will need to investigate this particular issue on your own or seek help from a developer should you not feel comfortable making these changes yourself. We do have an in-house custom development team that offer paid services, who may be able to assist. They can be contacted at [email protected] if this is of interest to you. If you have any further questions about the theme, we are more than happy to provide you with assistance on these inquiries.
Thank you for your understanding.