Learn English – A word to say many things should be done together

They are nearly synonymous but there are subtle differences.

Incremental highlights that the change was made in identifiable steps.

Gradual puts focus on the overall pace of change, which may by incremental or continuously slow.

Venezuela bagan incremental land reform in 1998 which led to a gradual reduction in productivity and increase in food imports.

In the context of a recipe specifically, just about every recipe I've ever seen written in English supplies the temperature value without any antecedent or substitution in the sentence ("Set the temperature to 450 degrees" rather than "Set the temperature to the required value"). "The required" or "prerequisite" offers a formal or technical tone that would look strange on a recipe or any other informal set of instructions.

You can use "the correct" or "the proper" ("Set it to the correct temperature") if you know that the reader knows which temperature you are talking about. If you wish to refer to something that you have already mentioned before on a written page, you can use "the above" (or "the below"/"the following" if you haven't mentioned it yet). Ex. "Set the temperature to the above value."

Often, in English, there is not any need for an adjective that describes the temperature we want because "the" is a definite article. As long as there is only one "thing" that we are talking about, "the" can be used to indicate it with no ambiguity. For instance, if you are writing a recipe for baking cookies, then the cookies are only going to be baked at one temperature (most likely) the whole time. Therefore, if you listed the baking temperature at the beginning of the recipe, you could say "Now, set your oven to the temperature," and the reader would know what you are talking about.