Yes, you can file your taxes first before sending Form 843. See the instructions below first.
Your employer is supposed to withhold 6.2% of your Social Security Wages (the Box 3 amount on your W-2), up to a maximum of $7,347 per taxpayer for tax year 2016.
If one employer withheld too much Social Security tax, you won't be able to take a credit for the excess on your tax return.
(TurboTax determines this by looking at your employer's EIN. In unusual cases where the employer changed their EIN during the tax year, an excess withholding credit can be taken as explained in "Multiple employers," above.)
So, if your employer withheld too much, contact them and ask for:
Do not file with excess withholdings on your return, as you may be subjected to penalties and interest.
What if my employer can't – or won't – cooperate?
You can correct the Box 4 amount yourself before filing. Simply multiply the amount in Box 3 by a factor of 0.062 and enter that amount or 7,347 (whichever is less) in Box 4.
To get a refund for the excess withholding, fill out IRS Form 843: Claim for Refund and Request for Abatement according to the Form 843 Instructions and mail it in separately. Make a copy to keep with your tax return paperwork.
Mail it to the service center where you would be required to a file a current year tax return for the tax to which your claim or request relates. So, mail it to the address that you would use to mail your Form 1040 federal tax return, which depends on your address. @dkrew72