It asks about residency at the beginning of the interview. If you need to change it, you can go to Setting Up> [Your Name’s] Province of Residence. If you are still in the first part of the interview and can’t see the Setting Up tab, click the “Back” button until you get back to the “Where did you live at the end of the year?”
If you are a non-resident:
When it asks you “What province/territory did you live in on Dec 31, 2017?”, choose which ever non-resident status you have (at the bottom of the list). Click the “Continue” button. Then on the “Let's get some information about your residency status.”, select “I was a Non-resident of Canada” and enter the name of the country you were in on December 31, 2017.
If you are a resident:
When it asks you “What province/territory did you live in on Dec 31, 2017?”, choose your province. Click the “Continue” button. On the “Did your Canadian residency change in 2017?”, select “Yes, my residency has changed.”. Then you will see a space to input when you entered Canada.