How to redirect certain IP to localhost

I want to block certain IP, and replace the Response with Block Page I made by Flask Server in localhost.
How to config that in Nginx.

For Example:

The program 'A' uses requests.get("http://123.123.123.123/GetInfo")
I want to replace the http://123.123.123.123/GetInfo with HTTP://localhost:5000/GetInfo
Is that possible for Nginx?

I can't change the source code of Program 'A'.
And I don't know what others program in my local will access http://123.123.123.123/GetInfo

I've tried the following configuration:

http {
    include mime.types;
    default_type application/octet-stream;
    sendfile on;
    keepalive_timeout 65;

    server {
        listen 80;
        server_name 127.0.0.1;
        location /GetInfo {
            proxy_pass http://127.0.0.1:6000/GetInfo ;
        }
    }

    server {
        listen 123.123.123.123:5000;
        server_name 123.123.123.123;
        rewrite ^/(.*)$ http://127.0.0.1/$1 permanent;
    }
}

It doesn't working.