Do you mean Line 31000? Line 31000 – Base CPP or QPP contributions on self-employment income and other earnings is automatically calculated if you have Self-Employment or other CPP pensionable earnings. CPP contributions are mandatory (unless you are 65 to 70 years of age and make a CPT30 Election), so the amount on Line 31000 can't be removed unless you remove the corresponding income.

This TurboTax Canada FAQ tells you how you can use ReFile: I've filed my tax return. Can I still make changes?