What is needed to remove my CPL restriction after becoming a US citizen?
You will need to pass the US commercial pilot test to remove the restriction.  If you have enough hours, you may want to consider applying for an ATP certificate.  

A couple of things are required to be completed.


Verify the authenticity of your foreign license through the FAA
https://www.faa.gov/licenses_certificates/airmen_certification/foreign_license_verification/
Complete an application for the new commercial or ATP license
Pass the appropriate practical test