The Student Loan field cannot be set to zero during setup if the option is active. However, since your new employee has no prior payments, you can easily bypass this by temporarily disabling the field to finish your setup.
To turn it off, here’s how:
Open the employee’s profile.
Go to Workplace pension, loan & other deductions and click Edit.
In the Loan status section, click the pencil icon, then uncheck the Student loan tick box.
Click Save then select Done to temporarily remove the field from the Pay history section.
Once completed, you can continue setting up the employee without entering a student loan amount. If student loan deductions are needed in the future, you can return to the employee profile and re-enable the Student Loan option.