Schedule 11 - Transfer or carry forward of unused amounts - 'Spouse or common-law partner' is checked and will not uncheck. How do I uncheck this box?

Go to your Deductions tab, Students - then drop down to Tuition CarryForward and Transfers will be under this tab. Whatever you have checked can be unchecked here, and that also means you will have to go remove the amounts applied in the Transfer tab as well.