Seat reservations are free of charge for users with a valid Easyjet Plus card.
Please first store your Easyjet Plus card number in your user account under "Loyalty & discount cards".
Now book your Easyjet flight as usual and select a seat. Attention! The price shown does not yet take into account the discount of the free seat reservation.
When you open the seat map, you will see the following notification:
The discount for the seat will be deducted as soon as you complete the booking process with "Complete booking", as shown in the following screenshot: