Refer to How to create a pay run? to create a draft pay run that can be edited.
Step 1: Go to "Payruns" and select the relevant pay run which you want to edit
Step 2: Click on the blue colour drop-down button next to employee's "Net Pay"
Step 3: Enter the "Hours" as 0 and "Base Rate" as the fixed value you wish to pay
Step 4: Click on "Save" to save the updated values
If you have any questions or feedback, please let us know via firstname.lastname@example.org