How do you conjugate the French verb agir in a feminine way?

The verb "agir" is already gender-neutral in French. It doesn't change its form based on the gender of the subject.

For example:

* Elle agit (She acts)

* La femme agit (The woman acts)

So, you don't need to conjugate it in a "feminine" way. You would simply use the regular conjugation for the desired tense and person.