There is no way to do what you are trying to do. The employer has to make the correction. You cannot do it yourself. It's not just that TurboTax can't do it. The reason that TurboTax can't do it is that there is no provision for it on the tax forms.
There is no place on a tax return to pay Social Security and Medicare taxes in your situation. Form 8919 is not appropriate because that form is for wages that were not reported on a W-2. That's why the income on Form 8919 gets added to your taxable wages. But your wages were reported on your W-2.
What would have to be done to correct the situation is more than just a corrected W-2. The employer would have to pay both the employer's share and the employee's share of the unpaid Social Security and Medicare taxes. And you would have to repay them for the employee's share that was not deducted from your pay.
I don't know what to tell you to do if the employer is not responding, or refuses to make the correction. There might not be anything you can do.
To avoid any further problems, make sure that Social Security and Medicare taxes are being properly withheld from your pay now.
