On my 1099-b, I sold mutual funds which were in an IRA. How do I show this distribution?

IRAs are not reported on a 1099-B.  Is it possible that your distribution was actually not an IRA?

Selling shares of a mutual fund in your IRA is not a taxable event and no1099-B would be issued. If however you sell the shares and take money out, a distribution occurs and a 1099R would be sent to you. No distribution happens unless you take cash or transfer shares out of your IRA.