For tax years before 2017, you will have to prepare your own return on paper, using the correct year forms you can download from the IRS, or you will have to see a professional. For 2017, 2018 and 2019, you can buy Turbotax as a download or CD to install on your own computer.
The good news is that, if you are out of the US for at least 330 days of the year, all your foreign earned income (income earned from working) can be excluded from taxation. Unearned income (investments, an apartment you rent to others, etc.) is still subject to US tax, as in any US-sourced income. So you might not owe much at all.
https://www.irs.gov/individuals/international-taxpayers/foreign-earned-income-exclusion
And for any year when you don't qualify for the foreign earned income exclusion, you still get a tax credit for foreign taxes you paid that will reduce your US taxes.
Another advantage of using a professional is that, if you do owe income tax, you probably owe a penalty that is larger than the tax by now. A professional may be able to help you negotiate a compromise.
