Anarchism is really against coercion, that’s what is meant by hierarchy. Hierarchy only makes sense if it’s used for coercion of other’s behavior.
There is no reason a group of people can’t organize in a voluntary hierarchy to complete a task without the use of coercion.
Imagine a group of 10 anarchist making pizza for the homeless. Two of them make pizza for a living and 8 are there for the week to help out. There is nothing preventing those 8 people from taking instruction from the two that know how to make pizza. Nobody is coerced to be there or to do anything.