where do 1099-K sales entered, I wish to offset these gains with am existing capital loss carry forward?

The reporting of personal item sales reports the sales on Schedule D where a capital loss carryforward may be reported.

In TurboTax Online, to report Personal item sales, follow these directions. 

• Down the left side of the screen, click on Tax Home.
• Click on the down arrow to the right of Review.
• Click on the blue band labeled Review.
• Down the left side of the screen, click Federal.
• Down the left side of the screen, click Wages & Income.
• Scroll down to Other Common Income click on the dropdown menu.
• Click Start/Revisit to the right of Form 1099-K.
• At the screen Did you get a 1099-K?, select Yes.
• At the screen How would you like to upload your 1099-K? click Type it in myself. 
• At the screen Which type of income is your 1099-K for, select the button for Personal item sales.  Click Continue.
• At the screen Let's get the info from your 1099-K, enter the information.     
• Click Continue.
• At the screen Personal Item Sales, you are told that further information will need to be entered.  Learn More provides detailed information for the next steps.  Click Continue.
• At the screen Your 1099-K summary, notice that the income relates to ‘Personal Items’.  Click Done.
• At the screen Your income and expenses, scroll down to Investments and Savings (1099-B, 1099-K….).  Click the down arrow.
• To the right of Stocks, Cryptocurrency, Mutual Funds, Bonds, Other (1099-B), select Start/Revisit.
• At this screen, you will be asked to Review the Personal item sales (1099-K).  Click Review.
• At the screen Now, enter one sale…., answer questions about the personal item sale.  Click Continue.
• At the screen, Let us know if any of these situations apply to this sale, sales expenses may be recorded.

The entry will be reported:

• on Schedule D of the Federal 1040 tax return, and 
• on line 7 of the Federal 1040 tax return.

Capital loss for a personal item sale reports $0 capital gain on line 7 of the Federal 1040 tax return.