Enter the sale using the "Stocks, Bonds, Mutual Funds, Other" interview telling TurboTax (I assume) that a 1099-B was received.
Fill out the information called for in the default "Security sale" TurboTax input form that comes up.
When asked when the stock was acquired type in the word "inherited". TurboTax will place this trade on Form 8949 as a sales category, i.e., long term.
Note:
A step-up in basis is the readjustment of the value of an appreciated asset for tax purposes upon inheritance. 1 The higher market value of the asset at the time of inheritance is considered for tax purposes. ... A step-up in basis is applied to the cost basis of property transferred at death
