You can't send data to an html file, only to a script.
You started right, change the html file into a php script.
This script can be used to print the first html page, and also to process the data when that page is submitted.
Tell the script to check if it was called by a submit button or not,
so you can decide if you need to process the variables.
Then, simply print the html page and use the cgi variables to fill out the form.
If you call the script for the first time, that variables will be emtpy so your form will be cleared too.