使用带有ajaxcontroltoolkit水印的jquery设置asp.net文本框值

I am using asp.net textboxes with ajaxcontroltoolkit watermark control. There is a list box with entries that can be edited using the text boxes. On selection change of the list box I need to set the text in the text box. I am using jQuery for this purpose.I am using asp.net textboxes with ajaxcontrolto