Bulk import historical buy and sell trades

I’ve used a CSV upload, and it worked very well. Unfortunately, I ended up with many, many duplicate transactions as I did not realise I had previous broker integration, so my CSV and broker transactions are duplicated for maybe 50-80 transactions.
Is there a way to reverse CSV upload? It would be horrible to delete individual transactions one by one.
Also, the help file indicates a limit of a maximum of 300 trades per holding and less than 3000 trades per portfolio, and file import limited to a maximum of 500 trades per spreadsheet file. Are these limits still current? I have uploaded just under 1000 transactions across two financial years successfully. However, arrived with many duplicates which I would like to undo, if possible, in bulk

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