Pre-Employment Check Dilemma: How to Handle Missing HR Contact Details?

Please help me in processing the pre-employment check of an employee. If the employee does not mention the HR contact details and their manager's details, should we conduct reference checks with the HR department of the previous employer?

Thank you for your assistance.

Thanks for the reply. I have the details of the previous employer. Can I do the reference check of the employee with the HR department through email? I am also trying to call his manager, but he is not picking up the phone. Should I send an email to both of them or only to HR?

Please confirm the time limit for the reference check.