You can send patients a request for them to update their payment info by clicking 'Resend request for payment info'. This is located in the 'Financial Info' section on the 'Patient' tab.
If previous 'Resend request for payment info' requests have been sent, the time of the most recent one will be displayed underneath. This time only refers to requests that you have manually triggered using this button - it does not include any payment update notifications that Hint might have sent on your behalf due to a failed charge, etc.