Passing Data from Input Field to Dynamic Text Box

Sorry guys if someone has covered this but I couldn’t find the answer in past threads.

Basically I just need information that is entered by the user into a input field to be passed to a dynamic text box.

Ie on a contact form when they submit their request a message is displayed saying "Thankyou{users name}, your request has been recieved.

The rest of the form is working, it’s just this bit!!!

Any info would be gratefully received.