You can use the left-hand navigator to return to the page where you entered your pension income.
There, you can amend or delete any amounts previously entered.
If you entered your pension income on a T4A, this page will be found at Income > T Slips > T4A Pension, Retirement, Annuity.
If you entered your pension income on a T4A(P), this page will be found at Income > T Slips > T4A(P) Canada Pension Plan Benefits.