Money transfers (where you own the money before and afterwards) are irrelevant to the IRS. You pay taxes for income, not for moving your own money around.
Your problem will be that you neglected to include it in your tax filings for the previous years, that's effectively tax fraud (and you could have even cheated yourself). You cannot simple ignore it in tax filings because 'it's in another country' or because 'you had it before'.
At the moment of sale, the money you get is compared with the buying price (even if that was decades ago before you ever thought about the US), and the gain is taxable income.
The recommendation is clearly to get your previous years' tax filing adjusted to include it. That's some effort, so maybe you should work with a CPA that has some experience.
Note: those are unfortunately hard to find and expensive for properties outside of the US, I tried for a long time and ended up doing it myself with tax software.