To do this you will need to change the deduction order and set 100% Tax Relief.
Deduction Order:
Select Payroll and then select Definitions.
Select Deduction Order Maintenance and then press Ctrl+M to enter Modify mode.
Find the Pension Deduction Ref.
Change the Order to Deduct so that it is higher (1 is the highest 999 is the lowest) than your PAYE Deduction.
Press EXIT.
100% Tax Relief:
Select Payroll and then select Definitions.
Select Deduction Maintenance and then press Ctrl+R to enter Range Mode.
Enter the Deduction Ref for Pension
Press F9 to search and then click Details 2.
Press Ctrl+M to enter Modify mode.
Click into the Taxable Relief % box and enter the value (normally 100%).
Do the same for NI'able relief % if this needs to be deducted before NI as well.
Press EXIT.