I have refilled for 2018,19 and 20 but cannot access 2017. Help please.
Unfortunately, TurboTax Online for 2017 has been discontinued, so you can no longer use it to ReFile your 2017 returns. However, you can still make adjustments to your 2017 return via CRA’s My Account which you can login to here: https://www.canada.ca/en/revenue-agency/services/e-services/e-services-individuals/account-individuals.html
If you don’t have a MyAccount login, you can also make adjustments to you return via the T1-ADJ T1 Adjustment Request, which you can find here: https://www.canada.ca/en/revenue-agency/services/forms-publications/forms/t1-adj.html