A climate champion will be able to act as a central focal point for your efforts to reduce your carbon emissions. It can be most effective to allow this person to receive special training and support and then share their insights with the rest of the organisation. They will be able to facilitate the work and have an overview of the process the organisation is making.
The first step is of course to find volunteers for the role of Climate Champion. Depending on the size of your organisation you might want to create a team who work on this. However it is helpful to have one person lead the efforts and be accountable.
Another crucial first step is to clarify what your Climate Champion is expected to do. Are they tasked with creating your carbon emission reports (link to action), organise an environmental audit (link to action), draw up your carbonisation plan (link to action) or simply create a list of potential improvements (link to overview of actions) in the organisation? Clarify with them what you expect your champion to do, maybe giving them a chance to prepare a proposal.
For their work they will need to undertake some substantial research, not only into the subject matter of decarbonising organisations, but also into the inner workings of your organisation. It might help to have someone with the necessary time and/or existing insights into the above.