TQ for your kind responses….
I fixed the errors after referring: [https://css-tricks.com/forums/viewtopic.php?f=6&p=14544] + some other factors.
the header function already tried, but not in the right place… that’s why i failed..
after submitted, form will be call [websitechange.js] which is external js file that contain thank you message.
I just modified the js file. [Problem Solved].
TQ for helping…. :)