If memory doesn't fail me (I'm not on my PC right now), I belive that requirements are selected at the unit you use to build/train the other units. So go to the barracks, and see where it you set the units it can train (if it is not there, then go to the abbility "training (barracks)", again I'm not at the Pc so I don't remember exactly where that is right now).
Anyway, where you choose what units the structure trains, you can edit the list and set the units you want, on each unit you can choose the requirements.
Each requirement is an individual entity at the data editor. Say you require the techlab AND the ghost academy (for Ghosts). Then thats ONE requirement that has both techlab and ghost academy (this is why GE Data editor is kinda gay...).
For your pyrobat, you can simply re-use the already made requirement of techlab.
If you want to create your own custom requirements, go to the data editor -> requirements, copy one (with similar properties, like techlab requirement) and then edit it. You can choose what unit/s you must have to train it.
To sum up:
- Create your own data entity in the "requirements" and create your own set of requirements (Everything you'll need for "x" unit, either 1, 2 or more structures, all in one entity) (unless that already exist, so you can reuse that).
- Go to where you choose units you train, and add/edit "X" unit and look for the requirement list, look for your requirement (either the one you created, or a pre-made you are using).
-???
-Profit.