You don't. If you take the entire rental property on your return and pay tax on any gain, what you give him is a gift. You are allowed to give any one individual up to $15,000 per year. If what you give him is more than that amount, you will need to file a gift tax return, Form 709. TurboTax does not support that form.
Form 709
The
purpose of IRS Form 709 is to report gifts that are subject to gift and
generation-skipping transfer taxes.
The
most common rule is the annual exclusion, whereby anyone can give up to $15,000 in cash or property to a person
without having a taxable gift. This is the provision that prevents most
ordinary holiday or birthday gifts from being taxable.
Even
if you have made a taxable gift, Form 709 isn't as big of a burden as many
think. That's because unless you've made a huge gift, you won't have to pay any actual gift tax.
The
U.S. has a unified gift and estate tax system at the federal level. Everyone
has a lifetime exemption from gift and estate tax -- $11.2 million for 2018 --
and even after you use up your $15,000 annual exclusion, any remaining gift
amount applies against your lifetime exemption amount.
https://www.fool.com/retirement/2016/11/11/2017-estate-tax-rates.aspx
