It depends whether you mean a general purpose or a specific one.
Way back in 1986 I experienced one of those 'Rebirthing' sessions where I was taken right back to the time I was born. The answer which came as a baby-voice from my own lips cried out. "Why do I make so many people miserable when - I was born to make people happy. That is what I was 'borned' for."
So, in my particular case, I believe I was born to "make people happy."
But how? How, specifically? Well, obviously doing the right thing by others comes into it. The adage, "Do unto others" and all that. But finding a specific purpose, that is often a more difficult thing to find out.
However, if you examine your life you will probably find you not only have a propsensity for a certain way of life but even a love of it. It will probably be something you've been pursuing as an interest or hobby for most of your life.
This could be your guidance; this the indicator. Go with it. If it feels right, it is.
With me, it is Communicating/Writing/Presenting/Teaching/Storytelling.
Find out what yours is and set to.