If using the online edition of TurboTax you can't edit lines directly. Line 23210 should auto-populate by entering the T4A (box 201 that directly affects it).
How to Enter T4A Slips in TurboTax online edition:
1. In the upper-right corner of your screen, select Find (magnifying glass).
2. In the Find window, type T4A Pension, Retirement, Annuity, and select Go.
3. Select Enter new T4A (or Edit if slip already entered).
4. Fill in all information from the information slip and scroll down to enter box 201.
5. Click on Done with T4A to save your entries.
6. On the next screen click on Done with T4A Slips.
You can then follow this TurboTax FAQ to view a detailed summary including line 23210: How can I see a detailed summary of my return in TurboTax Online?
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