How to redirect from plugin page

Added hook to process all form values and than redirecting as per process result:

Added below PHP code in theme/functions.php:

function process_form(){
 //code goes here
}
add_action( 'admin_post_appointment_form_process', 'process_form' );

And added/updated below html to form:

<form name="frm1" id="frm1" action="<?php echo home_url()?>/wp-admin/admin-post.php" method="post">
<input type="hidden" name="action" value="appointment_form_process">

Thanks for @Milo comment.