To amend a corporation income tax return you filed with Revenu Québec, you must:

• complete a new copy of form CO-17, Déclaration de revenus des sociétés (see courtesy translation CO-17-T), using the correct information (make sure you check box 24 to show that it is an amended return); 
• complete a separate copy of form CO-17.R, Demande de redressement d'une déclaration de revenus ou d'une déclaration de revenus et de renseignements (see courtesy translation CO-17.R-T) for each taxation year for which you are requesting an adjustment; 
• gather any documents justifying your request for an adjustment (related forms, adjusted financial statements, schedules, etc.); 
• place your documents in the order shown on the Filing the Corporation Income Tax Return and Enclosed Documents by Mail page (in French only); and
• mail the return and other documents to Revenu Québec.