If you have Past Service Contributions, it can be reported in different ways:
You either have a T4 with an amount in Box 74 and this amount is already included in Box 20 > so you enter both amounts in your T-slip information
Or you have a letter and the Pension contribution is not reported on a T-slip:
using the TurboTax Online > use "Find" on the top bar > search for "Registered Pension Plan" > check the box under the contributor name and continue to the next page > fill in the correct boxes
If you are using TurboTax CD/Desktop: > use "Find" on the top bar > search for " Registered Pension Plan" > Check the box beside "I made Registered Pension Plan Contribution for the current and past services" under the contributor name > From the right menu, open the RRSP profile, go to the "Registered Pension Plan" > enter your information
I hope this was helpful
