Redirect subdomain to subdirectory of same name

I've noticed that I've got a subdomain that used to exist and requires redirect to a subirectory of the same name, e.g. blog.site.tld is now www.site.tld/blog/ . A subdomain must be created in order to be recognized so that a redirection will work. But the subdomain creation assumes that a subfolder/directory is created off the root of the same name - which would conflict with the existing /public_html/blog/ directory. Hoping someone can provide a solution. Thank you!