What do I need to do when I sold and bought homes in 2017 for primary residences and failed to provide info to IRS?

Amend the return ... you must have gotten a 1099-S (so did the IRS) for the sale of the old home (buying a new home is immaterial) either at closing or the next January and you failed to report said sale so the IRS is now asking about it.  Some or all of the sale may be excludable however you must do the math to determine that ...

https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/00/27372

If the 1099-S was for the sale of your main home, it’s reported under Less Common Income in the Wages & Income section. Here's how to enter the form:

• Open your return.
  (To do this, sign in to TurboTax and select the blue Take me to my return)
• Type “sale of home” in the Search 
• Select the “Jump to” link in the search results.
• Follow the screens to enter the info from your 1099-S.

Profits of up to $250,000 ($500,000 on a joint return) on the sale of your home may not be taxable if it was your primary residence for two of the last five years. We’ll ask you some questions about the sale of your home to see if you qualify.

Other real estate sales

If your 1099-S wasn’t for the sale of your main home, select the option below for step-by-step instructions:

• Sale of a second home, an inherited home, or land
• Sale of a rental property
• Sale of standing timber