Chromium browser in WPF, how to set string to textbox?

Hi,

I am loading the .php page as a tabcontrol item using wpf Chromium browser, My .php page contains Textbox (id=mytext)

I want to set the value for the test box from C# code, 

How can I do this, 

I tried to search on google but not getting any related I am very new to chromium browser in wpf, and javascript,

Please help me to achieve this. Than in advance.