You can update an employee's direct deposit details from their profile.
Here' how:
In your left navigation bar, go to Payroll, then Employees.
Choose an employee.
From the Payment method section, click Start or Edit.
Enter their banking information.
Select Save.
In regard to the funds that were sent to their old account, if that account's closed or doesn't exist, it will likely be rejected by the receiving financial institution and return to your account within 7-10 business days. If it doesn't, you can consider requesting a direct deposit reversal.