As you may already know, the free plan allows you to create a maximum of 10 designs per account. Don't tell anyone but we are telling you a little secret in case you still want to create some banners.
The free counter is a lifetime counter there is no way around that and it means that even if you delete a design from your account you won't be able to create a new one instead.
Unfortunately, we cannot reset the counter for you but we want to give you a helpful hint, instead of deleting a design you can edit it and add new content and design.
Hope that helps!