You need to use TDM. We have a Cobol Lab in our TDM training. It is a good way to get started. It has a ramping up curve. You may need 2 - 3 days just to get familiar with TDM, go through the training, and then do your use-case.
Generally, you need to create all the structures you need in TDM. It depends on your copybook structure. And if it is a hierarchy of structures, you may need to build that first, then build a master structure in TDM. Then map the elements to your target.