If you have done the inventory and planning, strategy and planning, analysis and planning, impact analysis and planning outlined up to this point, you are ready to start the actual modifications to the code and data in your applications.
From these earlier activities, you should have a detailed implementation plan and source libraries ready to go and team assignments to match. The task at hand for these teams is to find each and every occurrence of the date impacts identified during analysis and change them according to the implementation plans, coordinating with the teams who are handling the interfacing workunits and partitions to build bridges and interfaces.