How do I change my answer on box 6a? I am being claimed by another taxpayer? I am NOT using the online TT version.

I am using the disc version of TT. How do I UNcheck box 6a (which I apparently checked erroneously or the program assumed the exemption without asking me)? The program does not ask the question in the step-by-step method and does not allow me to change it directly on the form.