The following step takes you how to Assign Company Code to Controlling Area in SAP CO step by step
SAP IMG Path: – SPRO >> Implementation Guide for R/3 Customizing (IMG) >> Controlling >> Organization >> Maintain Controlling area
In next screen double click on “Maintain controlling area”
Select the company that assign to controlling area and click the company code on the left hand corner
Click on new entries and update the company code and press enter to continue
Click on save icon to save the data. Successfully you have Assign Company Code to Controlling Area.