brokerages don't usually get this reporting wrong and make the appropriate cost basis adjustments. What level of detail are you looking at in the 1099B - you can have a wash sale on a position sold for a net gain, but on the underlying detailed tax lots some can have losses considered as wash sales that are disallowed and the cost basis has already been adjusted on other lots.
you keep referring to "entering a gain". you enter proceeds and cost basis, and adjustments for wash sales, AMD etc. TT and Form 8949 calculate the gain/loss accordingly. If the brokerage did make errors and you're having to calculate this offline for some reason, you should have all the fields you need. The screens are slightly different if you are entering it as Sales Summary vs. One by One.
