You report RRSP/PRPP/SPP contributions on the tax return for the tax year in which you made them. So you would need to go back to the return for the tax year you made the contributions in and add them. You also would need to change the following years returns to claim any deductions or add any carried forward amounts.
Contributions made during the first 60 days of the year are counted as being for the previous year. For example, if you made a contribution in February of 2022, then you would need to enter that contribution on your 2021 tax return.