After you file

There may be several issues.  You say you are "new to the U.S."  -- we do not know for sure because you have not told us your immigration status.  But if you are a non-resident alien you should not have used TurboTax.  If you are NRA you have to file on a 1040NR which is not supported by TurboTax.  

And when you mail a tax return you are supposed to attach your W-2's or any 1099's that show tax withheld.

TurboTax never knows about letters sent to you by the IRS or the state.  No information is provided to TurboTax after you filed your tax return.  What exactly does the letter say?  Is there a CP number or letter number up in the corner?

TurboTax does not receive any information from the IRS or your state after your return was filed, so no one at TurboTax knows about a letter you received from the IRS or the state.

(what the letters from the IRS mean)

I GOT A LETTER FROM THE IRS   

https://ttlc.intuit.com/questions/3605673-i-got-a-letter-or-notice-from-the-irs

I AM BEING AUDITED

If you purchased Audit Defense:

https://ttlc.intuit.com/questions/2924451-i-bought-max-or-audit-defense-and-now-i-m-being-audited

AUDIT SUPPORT

TurboTax has a special phone number for help with IRS/state tax letters, which will be easier than going through regular Customer Support.   At the page below, click on the blue button that says "Get Help from TurboTax Support".  Then it will ask you what tax year is your letter.  Then it will ask you what the letter concerns. Then it will show you the phone number during posted business hours.

https://support.turbotax.intuit.com/irs-notice/audit-support/