I received a letter adjusting my tax return for 2017.
TurboTax does not receive any information from the IRS about your return after you file it, so no one at TT knows anything about the letter the IRS sent you. Does the IRS say they received income information that was not reported on your 2017 return? Are they correct--did you leave off a W-2 or a 1099 of some sort?
You could get a free Wage and Income transcript to see what income was reported to the IRS by various employers and other financial institutions, etc for 2017. See if it matches what you reported on your 2017 tax return.