You need to change the value specifically using JavaScript , because The search form is generated by itself and there is no access to the code.

Thank you in advance.

Answer 1, Authority 100%

pure_js:

document.getelementbyid ('someinputid'). Value = 'Changed Value';

jQuery:

$ ('# SomeInputid'). Val ('Changed Value');

Answer 2

$ (document) .ready (function () {
 $ ("INPUT"). Val ("value");
});
Or
& lt; input onClick / Onblur = "this.value = 'values'" & gt;

It depends on what is your situation.
Do not forget to connect JQuery Library .