To link an existing allowance or deduction to a bank account select Employee - Modify Employee Details - Direct Credits.
Click Add for the Add New Bank Account screen.
From the resulting Add New Bank Account screen enter the Account Number you want the funds paid to.
From the same Add New Bank Account screen select Calculation Criteria then Linked Deduction.
Select the deduction to be linked to the bank account number.
Just about there!
Now the deduction is linked to a bank account number, a code and reference can be added as shown below.
These details appear at the recepients end when funds are received, meaning the recepient can correctly identify the payment.