Swapping liquid egg substitute for whole eggs is simple. Measure 1/4 cup substitute for every whole large egg in your recipe. It's true in reverse, too: Use 1 whole egg for every 1/4 cup of egg substitute listed in a recipe if you would rather use fresh eggs instead of substitute.
Add the substitute at the same step that you would add the whole egg. Easy!
But there are a couple of things to keep in mind when considering the swap.
Egg substitutes are about 99% egg whites with color added to make them yellow. Sometimes there are other ingredients added to make the texture better, bump up the nutrition, or kick up the flavor, like dry milk solids, vitamins and minerals, gums, and seasonings. Removing the yolk eliminates essentially all of the fat in an egg and consequentially makes egg substitutes cholesterol free. Good news for a lot of people, but if you are making a cake or quick bread with egg substitute, using only egg whites or liquid egg substitute will affect the texture of your baked good. Since egg whites are mostly protein, your cake or bread will bake quicker and quite possibly become tough, spongy, or dry. That extra bit of fat found in the egg yolk really adds tenderness and flavor to baked treats.