You include it on your tax return.
https://www.irs.gov/publications/p17
> Income from illegal activities, such as money from dealing illegal drugs, must be included in your income on Schedule 1 (Form 1040), line 8, or on Schedule C (Form 1040) if from your self-employment activity.
You're theoretically safe from them disclosing this to other law enforcement agencies. (I wouldn't want to test that, though.)
https://money.cnn.com/2013/02/28/news/economy/illegal-income...
> If you tell the IRS you made $1 million from stealing money or dealing drugs, does the agency tip off the cops?
> Legally, it can't, unless a law-enforcement agency gets a court order granting it access to a specific taxpayer's return. The IRS isn't supposed to proactively alert other agencies about misdeeds unless terrorism is involved. In that case, it still needs a court order to disclose anything, but the IRS can initiate the legal process on its own.