You should see a button near the top that says "Forms" ... when you click that, a list of forms comes up - the income forms usually show up first.
For example, your receipt for Old Age Security would be "T4-OAS".
Find the form in that list that has the exact same name as the form you have, click it - it will open, and allow you to enter the data that exactly matches the boxes on your pension income forms.
Good luck!
