Login to your Bitfinex account.
Navigate to the reports page and click on the dates in the top left corner.
Select the full date range of your trading (e.g. 2020 year)
MAKE SURE YOU SELECT:
Trades, MM-DD-YY format and enable DISPLAY MILLISECONDS
Click Export and follow the instructions to download your .csv.
Navigate to the Bitfinex tab on the Import Trades step and upload your CSV file.