This TurboTax FAQ has instructions on how to claim the Canada Caregiver Credit (CCC): How do I claim the Canada Caregiver Credit?
This TurboTax FAQ has more information on how to ReFILE your return to add this change: I've filed my tax return. Can I still make changes?
If you need more assistance adding this credit to TurboTax, please contact our phone support team at 1-888-829-8608.
For tax returns from 2017 You would need to change them using the Canada Revenue Agency (CRA)’s My Account service or send in a request by mail, using a completed Form T1-ADJ, T1 Adjustment Request.
You can log into the CRA’s My Account service on their website: My Account for Individuals
You can download the T1ADJ from this CRA webpage: T1-ADJ T1 Adjustment Request