The existentialist view, epitomised by Nietzsche, is it means:
Become what you happen to be, not what you think you should be.
Don’t pretend to be something you aren’t or can’t be, don’t strive to be an ideal version of you, and simply go with who or what you are.
The essentialist view, more in line with Plato and Aristotle, is to:
Become such as you are, having learned what that is.
This is the opposite of Nietzsche. It suggests you find out who you really are and then work towards this, and don’t be sidetracked by your baser drives.
There is also the argument made by Josh Cohen in The Private Life: that we can’t actually ever know our own, unconscious selves. Even if we could know what our true self is, Cohen’s suggestion is that we can only ever know the bit above the surface – we can never understand, perhaps in a way a friend can, why we pursue doomed relationships or reach a self-limited plateau in our work.
I tend to fall more towards the existentialist view here. Even if I could identify what my true self was, I’m not sure I would either, first, know when I’ve reached that state, or, second, not be diverted away from reaching it by how I am.