Learn how to change the privacy settings of your Facebook event from “Private” to “Public”. Although you cannot change the privacy of an event once it's created, you can duplicate it (along with its guest list) to create new privacy settings.
Steps

Step 1. Go to https://fr-fr.facebook.com/ in a browser
You will need an internet browser to use this method.
- When you see the home screen, enter your username and password at the top right of the screen, then click Log in.

Step 2. Click Events
It's in the left menu below the title To explore.

Step 3. Click on the name of your event

Step 4. Click ⋯
It's to the right of the button To modify below the cover image.

Step 5. Select Duplicate Event
A new window, that of the duplicated event, is then displayed.

Step 6. Select Public Event from the drop-down menu
This can be found at the top left of the event window.

Step 7. Enter any additional details and click Create
Everyone you invited to your original event will now receive invitations to your new public event.