For creating usernames and passwords for your customers, you will need to get SMS or Email Notifications.
When you enable the Access to Customer Panel notification action, this action will send Username and Password to your Customers. There are two shortcodes. {customer_panel_url}, {customer_panel_password}
The first one is for the URL of your Customer Panel. The second one is the randomly generated password for their username.
Once they log in to their account with the password that is automatically generated by the system, they can change their password. Also, their email will be their username. So, please keep the email tab as a required field at the Booking panel. Your customer can log into the system using the WordPress login page.