header("location:index.php") কাজ না করার কারন কি?

Never use any white spaces or print anything before calling header() function. If you use header function in any php file, PHP processor never expect any output before header() function.

Careful of including php file to another file if included file is contained header() function.  File must not echo or output anything before include the file which contains header() function.

local server is also web server which is called localhost or local webserver

You just simple mistake. set         header("Location:index.php")