To set up a pre-defined picklist for Cost of Sales, from the menu:
Go to Settings
Admin settings > General Settings
Look for 'Cost of Sales'
*If this setting is not available in your account, please reach out to email@example.com to enable this for you
To create the options:
Click on 'Add new'
Input the value
Select the check-mark to save
These options will be made available in the placement / compensation pages for user selection: