I see no way of entering anything on Schedule 1 line 24z regarding a 1099-K and I see nothing in any IRS publication that indicates you should.
If you want to enter the 1099-K and the adjustment, you can follow the instructions Stevos555 provided.
Instead of a negative adjustment on Schedule 1 line 8z, Schedule 1 line 8z will report the net amount.
The included supporting details document will supply the details concerning the adjustment if you want to be sure the IRS has that information.
The 1099K needs to be entered on the Business Income screen.
This can only be accomplished using TurboTax Home & Business Desktop.
According to the IRS:
"The Form 1099-K is an information return. Use this information return in conjunction with your other tax records to determine your correct tax. To get further information on record keeping, check out Publication 552, for individuals or Publication 583, Starting a Business and Keeping Record."
IRS LINK
The only mention of 1099-K in IRS Pub 525 is the following:
"Generally, if you work in the gig economy or did gig work, you must include all income received from all jobs whether you received a Form 1099-K, Payment Card and Third-Party Network Transactions, or not. See the Instructions for Schedule C (Form 1040) and the Instructions for Schedule SE (Form 1040)."
PUB 525
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