Our destiny is determined at the time of our birth. Planetary placements in a birth chart result from past karmas and point to possibilities of our actions if we do not change our outlook. For example, you see money lying on the street. You have three choices born of free will: pick it up and pocket it. Donate it to a needy person. Or leave it lying there. Each action has merit or demerit.
Free will is a powerful force; it’s about the conscious choices that will either mitigate bad Karma or add to it. So, fate or destiny and free will are intertwined. The more you make ethical choices out of free will, the more you alter your future.
So, do good, think pure thoughts, and lead an honest life. You can undo your past-life Karma, and the choice is yours.