Tax Planning for You and Your Family 2019 by KPMG. p 59.
If you receive a lump-sum pension payment relating to prior years, you may ask the CRA to determine whether it is more advantageous to you to recalculate the tax on that income as if you received it in those prior years. This measure is intended to relieve the higher tax liability that may result if the entire lump-sum is taxed in the year of receipt, rather than year by year as your right to receive the income arose. Eligible payments must total at least $3,000 in the year and include superannuation or pension benefits (other than non-periodic benefits), wrongful dismissal and other employment-related payments arising from a court order or similar judgment, and certain other amounts.
How do I ask CRA to do the emboldening? I have an online CRA account. What to click?
Why doesn't CRA just do this automatically without being asked?