How to prevent duplicate record insertion after refreshing php page

Hi, If I do refresh after submission of a form, records are getting stored multiple times. I have two pages. /submission-form/ and /thank-you/ I was trying header('Location: /thank-you/'); on submission-form page after successful validation and insertion into db. Still if I do refresh on thank-you page it adds one more record in database. How to prevent it without token? -- Devendra Jadhav देवेंद्र जाधव