According to Canada Revenue Agency (CRA), you can. CRA link to more information: Simplifying the process for claiming a deduction for home office expenses for employees working from... 

Please follow the directions in our TurboTax video How to claim your Covid-related employment expenses in TurboTax | TurboTax Canada

You can adjust your 2020 tax return. How you file your adjustment depends on how your original tax return was filed, and whether it was a federal or Québec return. Instructions on filing adjustments for both scenarios are provided below.

If you filed your original return using NETFILE:

1. Sign in to your TurboTax Online account for the tax year you want to prepare an adjustment for
2. In Return Manager, select ReFILE beside the filed tax return you want to adjust

If you printed and mailed your original return or are in a situation excluded from ReFILE:

1. See the CRA’s How to change a return page to make an adjustment online in your CRA My Account or by mail

For more information here is a TurboTax FAQ: I've filed my tax return. Can I still make changes?

Thank you for choosing TurboTax.

This absolutely worked for me. Once I discovered ReFile I was off to the races. The dollar figure CRA worked out is nowhere near what Turbotax and I came to so I'll wait to see if that changes as the express file was instantaneous. I expect I may need to make a phone call.  Thanks for your help!