Where do I enter purchase dates for a stock sale that is showing as Unknown Term Basis on the imported 1099-B in Turbo Tax? Do I change the 1099-B? Or elsewhere?

To change:

1. Go to federal
2. Wages and income
3. Investment Income
4. Stocks, Cryptocurrency, mutual funds etc.

The first screen is a summary screen of all your 1099B transactions. Click edit on the transaction(s) where the change(s) is/are needed. The purchase date is reported in Box 1B for each sale and can be changed.

Thanks @DaveF1006. That is helpful, but I guess what I'm really asking is, do I change the basis of my reported PTP shares on the 1099-B or do I do it elsewhere, such as Form 8949 or 4797? The "cost basis not reported to IRS" box is checked on the 1099-B. But when I leave the cost basis blank in the 1099-B, and then adjust it few steps later, Turbo Tax flags it as an error. Is it okay to put my own CB in on the 1099-B, changing what I imported from the broker?

If I go ahead and do that, entering the Cost Basis as reported in Column 6 of my K-1, that seems to put the correct amounts in the correct column on Form 8949, as the K-1 instructs. However, I've also got amounts in the Column 7 on the K-1 "Gain subject to recapture as Ordinary Income". It says this should put put in Form 4797 Part II Line 10, and Form 8949 Column G as a negative adjustment. I can't figure out how to make that happen in Turbo Tax. :(

For non-covered securities ( BOX B or E) showing zero (wrong) basis, enter the correct basis yourself.
Use code "B" and put -0- in col (g).

Let TurboTax put in the proper code.

@Fezziwig 

@fanfare I revised my question. See above. I'm getting quite confused.

Here's the problem with putting -0- in column G... My K-1 shows "gain subject to recapture as ordinary income" amounts that need to go into Column G. Trying to figure out how to get those in the right place. Where to enter them?

suggestion-

File form 4868 request extension of time to figure this out.

you still have to pay tax due now.

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-- if the ordinary income amount is shown on Schedule B  Form 4797 Part II Line 10,then enter cost  as needed to reduce the gain on Form 8949 with no adjustment

If it's not there, enter it manually

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you need a code for Col F if you want an adjustment in Col G

do you know what code you need?

TurboTax won't allow all the codes, Code B is a special case.

you have to go through step-by-step to find "more info" or "special Cases"

that allow you to do this

Code "O" Other would be a choice, but I'm not sure TurboTax allows that one.

@Fezziwig