In order for an employer to be set up to receive duplicate statement information, you will need to have them prepare a FINRA Rule 3210 (formerly NYSE Rule 407) letter which confirms your employment and which serves as their request to receive duplicate statements and trade confirms. The Form 407/Employer Email can be downloaded and then uploaded on your account using the Upload Documents tool on the IBKR website.
You may wish to first verify with your employer if they are a participant in the IBEmployeeTrack program which automatically identifies new IBKR accounts opened by employees and organizes into a single daily transmission of the reports required for all.
If you wish to confirm whether or not your employer is receiving duplicate statements, you can contact IBKR Client Services. Please select Account Services as the ticket category followed by Regulatory and type "Employer Duplicate Statements" as the subject.
In case you changed employer, first ask IBKR to stop sending duplicate statements to your former employer and then complete the procedure above.
Find more information on the Rule 3210 page of the FINRA website.