Add 2 by 4 inch framing boards on 16 inch centers to fill in the wall area.
Infill garage door.
As the foundation to the existing garage is not likely to be traditional it s probably a shallow slab a new foundation may be needed for the new wall.
Depending on exact door size.
For single size door infill weight should be between 6 and 10 kg sqm.
The open for infill door ofi gives all the benefits of a manufactured canopy or retractable door mechanism and locking.
Nail up framing consisting of thicker boards if you wish to add extra insulation.
As the foundation to the existing garage is not likely to be traditional it s probably a shallow slab a new foundation may be needed for the new wall.
Include window space in the framework if you will install a single window or a larger window section.
With the garage door removed attach a pressure treated bottom wall plate to the concrete to be used for the new wall.
In fill garage door as part of the garage conversion it is likely that the original garage door will be infilled with a new wall and possibly a window or door.
If the garage has a support column build a temporary bridge support by doubling up some 2 by 6 temporary headers and wedging them under the garage door header with 2 by 4 stilts on either side.
As part of the garage conversion it is likely that the original garage door will be in filled with a new wall and possibly a window or door.
Take down the garage door and tracking before you implement the framework plan.