You need a Doodle account to edit your poll. First make sure you are logged into your account, or create an account here
Be sure to open the poll in admin view - if you created the poll from your Doodle account, simply click on the poll from your dashboard. Otherwise, you can click on the link in the email you got after creating the poll. If you no longer have that email, you can have it resend here.
Click on "edit" at the top of the page, or find it under the "more" menu.
You can now edit your poll. You can remove whole days by clicking directly on them in monthly view, or delete individual times by clicking on the little x next to the times in both monthly and weekly view. If you want to add dates, simply add them the same way you did when you created the poll.
Remember to go through the remaining steps to save the changes you made.
If you add new options, please be aware of the question marks issue.
If needed, you can also edit the time zone (as long as non one has voted in the poll yet). Read more about time zones and how to edit it here