i am trying to turn on Find My for my iphone, how to find iphone passcode

You don't know the 4 or 6 digit passcode you used to set up and sign into your phone? If you don't know it, no one can tell you what it is. And you'd have to erase your phone completely using your computer with iTunes if you need to set it up again with a passcode. And you have to have a passcode for Face ID to function on your phone. Such an important piece of security should have been written down somewhere safe for future reference.

Please clarify.

Have you forgotten the passcode for you phone?

Do you have possession of your phone?

You need to have physical possession of the device and sign into your iCloud account to turn on Find My.