You can easily password-protect your event and require attendees to enter a password that you create.

To enhance the security and privacy of your event:

Step 1: Locate Security & Passwords under your Event Settings

In your event's left navigation menu, locate Setup and select Event Settings. From there, select Security & Passwords.

Step 2: Set a password

Create a custom password that attendees will have to enter upon registration. Remember that passwords are case-sensitive and must be at least 4 characters.
You're free to change the password for your event at any time. Just be sure to share it with anyone you previously shared it with if you still want them to be able to register.

Step 3: Save
Save your password and test your form. This is what your guests will see when they enter your event's URL:

You can control the message your guests see above the password entry field in Event Settings > Language & Translations.