> and I want to click Search button on home page automatically every time once a user login to this application.

This is not “what” you want to do. This is “how” you want to do it.

> I need to do this to submit the values of select list item.

This gets more to the “what”. But again, it’s not about “submitting” values. In APEX, items have “session state”. Session state can be thought of as the value of an item that’s used during a page rendering or page processing.

There are various ways to set the session state of an item. Submitting the page is just one way. Another way is to use an “on load” computation or process. If this is done prior to the region rendering, then the region will use the new values when rendering.

If you only want to do this once when a user logs in, consider creating an application level (in the Shared Components) process or computation with the Point set to After Authentication.