You can also add it in the same line, you don’t need a separate line, just add it to the end like this
PublicDependencyModuleNames.AddRange(new[] {"Core", "CoreUObject", "Engine", "InputCore", " SimplexNoise"});
This is an exact replica maybe with few other options of other versions I have seen online googling it , made to work with Unreal, so you can dig online about additional things if you like.
Also I would check the plugin setup after you install it, sometimes it does not activate, just type simplex in the plugin section to find it after you install it and if it’s unchecked check it.