Environmentally in this context just means anything that's not directly genetic or inherited epigenetic. It doesn't mean plants and animals or anything like that.

IQ is mostly genetic (in rich egalitarian countries like the USA), but everyone seems to agree that there's still some environmental factors that smart parents can do to make their children a tiny bit smarter. I don't know exactly what those factors are though. Probably any kind of practice with thinking and studying would help a tiny bit, but perhaps other things to do with better care such as nutrition. But I know there's not a lot that parents can do that helps with IQ long-term, especially when society as a whole is already trying to do everything they can to boost IQ environmentally already.