Creating Subdomain and wp-login issue

Hello, guys!

I have tried to create a subdomain of my main website but something went wrong on the way and I can’t figure it out. First of all, let me tell you what I did and how I want the subdomain to work.

I have created new database and install a new WordPress site on a specific directory ( e.g. public_html/blogosaur), then
I created the subdomain (e.g blog.example.com) from the cPanel and set the Document Root (from cPanel) to public_html/blog . I wanted that the directory root name from public_html to not have the same name as the subdomain for security reasons.

It went perfectly until I saw that when I tried to access my new Blog (blog.example.com), the browser was opening example.com/blogosaur directory which I didn’t want. I wanted it to open the subdomain, blog.example.com, not the example.com/blogosaur.

I thought that maybe I have to do some settings from the Dashboard and I changed some settings: Setting=> General and changed the WordPress Adress (URL) from https://example.com/blogosaur to blog.example.com and Site Adress (URL) to https://example.com/blogosaur , and this was my undoing.

Now I cannot login as Administrator because I cannot access /wp-login anymore, but I can still visit the website.

First, how can I fix the issue with the /wp-login and then, how can I properly setup my subdomain in order to be as in this example: blog.example.com , but the public_html directory root name to be blogosaurus?

Sorry for my English.