Go to your event
Go to settings
Go to tickets & products
Select 'add ticket' or 'add product'
To create the Early bird ticket you need the settings in the "more options" field.
Create a separate “Early Bird” ticket/product with a lower price.
Click on "more options"
Use “Available amount” to limit how many early bird tickets can be sold.
Use “Stop sales” to automatically close early bird sales a certain number of days or hours before the event (e.g. 30 days before the event starts).
Use “Visibility” to make sure the ticket is available online (or POS if needed).