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Happy to have you here on the Community page, @prapsaru.
If the transactions are manually entered in QuickBooks Online (QBO), you can go to the register to delete or remove the duplicate transfer transaction.
If the transactions were downloaded from the Banking page, you can undo or exclude the transfer from the Reviewed column.
Post again if you have any other QuickBooks or banking questions. I'm always here to help however I can. Happy weekend!