At a high level, it is possible to define a general approach for agile transformation that applies to most situations. But one level down from that, things vary tremendously.
There are many general models and approaches for managing change in an enterprise. Lean thinking. Satir Change Model. Adaptive Management. Aspirational Envisioning. Transtheoretical model (TTM). Kotter. BTMM. Accelerating Implementation Methodology. Maslow's Hierarchy of Needs. ADKAR. Shu-Ha-Ri. Agile Fluency. Ken Schwaber's "Playbook for CXOs". Mike Cohn's model. Cotter. Five Rules for Learning. Devops. Holocracy. The list goes on and on.
All of these have potential value for thinking about how to assess the situation and how to go about planning for and executing change, but none of them is a plan. To create a plan, you need to talk to a-lot of people in the organization and come to understand the circumstances. Then you are ready to create an initial plan, and it will be wrong - and that's ok.
The important thing is to think. What are the politics in the organization? What are the incentives? What are the main impediments? What is working now, and what needs to change, and in what order? What are the current constraining factors? What will they be a year from now?
Think through these things, discuss them with the CIO and the rest of the IT leadership team. Talk to teams. Talk to functional managers. Sit in on key events such as software release meetings and release planning meetings. Sit in on some program planning meetings. Sit in on the CIO's staff meeting, to get a feel for the other strategic issues. Sit in on portfolio planning sessions. Sit in on other key meetings as you discover them.
In the words of Caryn Waller, a business, product and marketing executive consultant with 18 years of experience in mobile, media, telecommunications, internet and software development,
"Speaking from personal experience I've worked for large and small companies of different cultures and had to bring about change and used different strategies on each occasion. There have been tactics I've employed over and over but interestingly they were invariably chosen for different reasons and even then I personalise it to fit the individuals in question. There is no one-size-fits-all for change as change starts with the current human perception which is unique."
This means that focusing on one aspect of the problem will not succeed. Durable change must address behavior and habits. It must address organizational incentives. It must address business processes. It must address learning. It must address organization structure. It must address all these things - not necessarily all at the same time, but that is where the planning and execution come into play.
According to William D. Eggers and John O'Leary, authors of If We Can Put a Man on the Moon: Getting Big Things Done in Government, planning is crucial but execution is everything; extremely successful large projects, even going way back, such as the Marshall Plan, were built on a process of planning, doing, evaluating, and then adjusting the plan and continuing, and great attention was paid to execution and on the ground realities.