How do i add a text "like search01 server" in the search dashboard, so when user log in search head, they know which server they are in the pool.
I'm a bit confused by your question. Are you trying to put the literal string "like search01 server" anywhere on a dashboard? Or are you trying to put it as the default text inside a search's input bar?
In web.conf you can add a key called login_content, and it will add a message on the login page.
But anyway the easiest way is to put the message on the login page, like this:
[settings] login_content = <h3>this is search01</h3>
also appears in some other answers.