If bias exists it is culturally and biologically motivated and that can only be fixed by changing the culture significantly.
Women in free cultures do not like STEM. That is a fact. In countries where gender roles are being silenced (that's a good thing) women dislike STEM even more!
I went to a STEM focused high-school that had equal numbers of women and men (3000 students). Not the same percentage went for STEM fields after graduation. Women were also more successful during high-school. Every year the questionnaire confirms that women just aren't interested in STEM and go to fields that deal with people much more (medicine and similar social fields - rehabilitation, working with children with disabilities, social work etc.))