wp query – checks if a form has been modified after sending

I have a form, the user selects options and entries, and then clicks submit. after sending, the user will see the requested messages (depending on how he / she filled the form);
the problem is that when it goes to the next page, if the user changes the form and clicks submit, he / she will see the corresponding message, but on the same page as the last form.
if I could understand if the form is verified. everything was fine.
Thank you so much.