Making blog page menu selected on single post page

Hi
I have created menu in functions.php using

register_nav_menus(
			array('my_nav'=>'My Navigation Menu')
		);

and added menu from admin panel and I am using static home page and showing posts on blog page eg https://mysite.com/blog. Now when I open this page I am able to see all the posts and this blog menu item is selected but when I view post that is on https://mywebsite.com/blog/first_post/ the menu item is not selected. All I want is whenever user is viewing any post the blog menu item should be selected.
I am using this /blog/%postname%/ code in custom permalink.

Please help me.
Thank you.

[No bumping, thank you.]