When you select no to 'Someone else can claim me on their tax return' in TurboTax then you will be claiming yourself and line 6a will be checked.

Follow the steps below to change whether or not you will be claiming yourself (line 6a) 

1)    Sign into TurboTax Online

2)    Continue your return by click My TurboTax > Tax Timeline > Take me to my return.

3)    Go to Personal Info > Personal Info Summary > and click Edit to the right of your name.

4)    Scroll down to Question 3 - Someone else can claim me on their tax return.  

               a.       If you select yes – line 6a will be unchecked - someone can claim you

               b.      If you select no -  line 6a will be checked - claiming yourself