Once you have realised the Macro Botanist skill, you will be able to view recipes to create macro-organism seeds from the crafting window, under recipes.
The macro-organism seeds contain the organism that when released on a planet will grow to a macro scale.
Your character will periodically create the Macro-organism Construct consumable, which is a part in all recipes. The other consumable parts you will need to purchase or gather in any way you see fit.