To get to the relevant section in TurboTax Online:
Select Tax Home in the left pane
On the Hi, let's keep working on your taxes! screen, select the dropdown on the right side of the State Taxes box, then select Start, Continue, Pick up where you left off, or Review/Edit
If you land on a New York interview page, select Let's get started, Continue or other similar prompt. Otherwise, in the left pane, select Prepare State, then proceed through the New York screens
Proceed through the state screens until you get to the New York Income Allocation screen
Answer No to the question, Were all of your wages and/or self-employment income earned in New York State?
On the screen, Form W-2 Summary, select Edit next to any W-2s you need to allocate.
On the screen, Allocate Wages to New York, you can choose one of the following allocation methods:
100% New York State income
Allocate by number of days
Allocate by percentage
Don’t allocate this employer
Allocate over multiple years
On the Form W-2 Summary screen, select Done.
On the following New York Income Allocation screens, enter the amount of federal income earned from New York sources.
If none, enter 0.
On the New York Nonresident Deductions screen, enter the New York State part of federal deductions.
If none, enter 0.
Follow the on-screen instructions to complete your return