If the cashless sale was reported to you on a 1099-B then enter the sale using the "Stocks, Mutual Funds, Bonds, Other" interview. A "same day" sale like that should, typically, result in a small loss due to selling commissions and fees.
If you didn't get a 1099-B - brokers aren't obligated to prepare them in this situation - then you don't have to report the sale, but if you do want to report you still use the "Stocks, Mutual Funds, Bonds, Other" interview and tell TT that you didn't get a 1099-B.
That's what get information onto Form 8949.
Tom Young