Why does form 8949 has a double entry for same amount?

[TomYoung]

This is a user to user forum and nobody here can see your income tax return or your computer screen.  So all we can do is make guesses.  One guess is that you both entered a trade manually and imported the 1099-B containing that trade.  Another guess is that you sold an ETF organized as a grantor trust or partnership and reported that sale using the Schedule K-1 interview AND that trade was also on a 1099-B you imported.

If you've really got a trade reported twice then delete one or the other of the trades.  If you used the Schedule K-1 interview to enter the sale of an ETF then delete the broker's report of the trade as that 1099-B won't have the correct cost basis figure.

[MaryS12]

Okay.

So I need to delete an entry; I found both and yes one has a negative cost basis which made for a $24000 capital gain.

Is there a menu that TT has that will direct me?   I'm concerned about "messing up."

I printed a X1040, wrote my explanation, printed the 8949 page for each entry.  However,  I'm not sure how to indicate/enter where the change on the taxes occurs.   Does TT do this for me?   (I assume eventually it effects net taxes but does it change cap gain/loss, then go somewhere, and then net which should give me carry over and a refund.... I guess I want to know what TT will do.)

[TomYoung]

If you go through TurboTax's "amend" process TurboTax creates a new Form 1040 with all of the correct numbers on it and all the Schedules, Forms and worksheets that support the new Form 1040.  It also creates a Form 1040X which you send to the IRS, along with any Schedules and Forms that have changed  from your original "as filled" income tax return.

When you start your income tax return the following year you transfer the amended income tax return, not the "as filed" income tax return.  That ensures that any and all carry forwards are properly stated in the new income tax return.