Filing as a dual status residents

I was on F1 Visa till 09/30/2020 and my status changed to H1B on 10/01/2020. I will qualify to make the first-year choice on April 1st, 2020.
As I am single, I don't qualify to make a full-year resident choice.

What I have understood till now that I have to file Form 1040 as a tax return and form 1040-NR as a statement.

My questions are
1) I tried to file form 1040 using TurboTax but the form was filled as if I was a resident for the entire year. Do I need to adjust these numbers by myself?
2) Showing 1040-NR as a statement - I found this line very vague. What does mean by the statement? Should I fill out the entire form or some specific details?
3) At some of the places, it was mentioned to provide a first-year choice statement. Is this statement alternative to Form 1040-NR or supplements the form 1040 and form 1040-NR?