Choosing a stock from a different slot for Tax return when 1099 shows different cost basis.

[gtushar1991]

I have a stock account with fidelity:
I sold stock A at a short term loss of $10
I sold stock B, and fidelity chose FIFO and showed a long term gain of $20
this makes my total capital gain of $10 long term

If I had chosen a different slot for stock B, I can have a short term gain of $10 
this makes my total capital gain of $0, and I don't owe any taxes.

I asked Fidelity to change the slot for Stock B. But they said the sale is settled and they can't do it.

My question is: at the time of tax filing, can I choose the date of acquisition and cost basis from another slot in my possession for Stock B, even though 1099 shows a long term gain on Stock B?


I sold some stocks in 2023, and fidelity by default chose FIFO, and Fidelity shows a "long term gain" on that. 
In another transaction, I have a 

[fanfare]

The basis shown is reported to the IRS.

If you want to sell a diffent lot (not slot) you have to inform the broker ahead of time, or change your default setting.

@gtushar1991