使用按钮更新templateField中的文本框

it's my first time asking a question here in stackoverflow so please bear with me. I am creating a webpage using asp.net, I have GridView with columns set as databound except 1 template field, within the template field is a textbox and a button. I want to update the value of the textbox using an outside button(a button in the same page, but outside the gridview), can anyone show/tell me how to do that? it's my first time asking a question here in st