The Social Security Number (US) or National Insurance (UK) number can be added to a candidate's profile while adding them to the platform. It can also be added/edited after the profile is already created on the platform. In order to add/edit it after the candidates' profile is already created, go to the candidates' profile (Candidates >> All Candidates >> eye icon against the candidate) >> General tab, edit it and click the Save/disc button (SSN will show for US, and NI for UK).
In order to add the Bank account details to the candidates' profile >> Billing Method >> select the Method from the drop-down. The options on the drop-down list in the screenshot below might be different for you based on your country.
After you select the billing method, you will get the fields to enter the Bank account details.