After a form has been successfully submitted you can choose to redirect the user to another page or URL or just show a thank you message (default option).
To redirect a user after a submission has occurred do the following.
Navigate to the Sign Customiser admin for your store.
Click on "Customisers" in the home menu
Click on the customiser you wish to edit
Click on "Forms" in the left-hand side navigation menu
Click on the form that you wish to edit
Scroll down to the bottom of the page to card titled "After Submission"
Make sure "Redirect to a page" is selected
Fill in the input named "Redirect URL" with the full url of the page you want the user to be redirected to.
Click save at the bottom of the page.