Received a corrected w2 after filing that shows a corrected 401K withholding and no other fields. How do I enter this? Do I assume all the other numbers stayed the same?

I have tried amending my return, with the corrected W2 our deductions were reduced from 16000 to 11000 also, which confuses me.  How could less withholding for 401K contributions mean less deductions?

Don't know if I entered the corrected w2 correctly, since it only showed the corrected field (12a), wouldn't box 1 change also?