For a 2022 backdoor, you would be entering the nondeductible new contribution on line 1, and the basis amount that already exists is line 2. That gives line 3 a total of basis in the Traditional IRA account.

The total converted isn't this part.

"The client strted in 2019 to 2022 total contributed 4X$6000=24000"

Then you don't really have a "backdoor" from the perspective of Backdoor. You have a partially taxable conversion, most likely, because their funds from 2019 and later were sitting there generating earnings, right? That means any conversion now, even if the same amount as what was put in for 2022, is a pro rata conversion.

Unless you are describing that every time they put into a Trad IRA, it was nondeductible and also immediately converted in full to Roth, and your "4X" is activity, not running balances?

yes, the client made contribution then converted immediately.

I am confused the system carried the 2021 basis to line two, so the total basis on 2022 is $12000

"2019 to 2022 total contributed 4X$6000=24000"

There is no accumulated total if, every year, they contribute and immediately convert; then every year the FMV (and basis) at the end of the year is $0. That means the starting basis of the account for any tax year is $0, as well. The contribution + that $0 is the total basis for that year, but ends at $0. And the amount converted is that same amount contributed, and since it is all basis (no time delay for any earnings), there is nothing taxable. That's how backdoor works.