Subdomain to point to post inside existing wordpress site

Hi Guys,

I have a website, which contains many different ‘pages’ including a page setup to take the posts. right now, you can access that page my going to https://www.mysite.com/blog. i want to forward my old blog (blogger) to this page, but have to use a sub domain address. i have setup up blog.mysite.com in my cpanel, but it is not pointing to the existing mysite.com/blog. instead it brings up a forbidden page. any thoughts how i can make this work smoothly –

thanks!!