To extend the end date of a project or reopen a closed project (having reached its end date), login to your fundraiser account and view your project page as your donors would see it (My Projects > click on the name of the project).
Click on "Edit details" below the Give button. Update the Deadline field and when done, click on "Save changes".
Note: When a fundraiser project reaches its end date, all recurring donations are automatically stopped and the donors responsible for them notified. Supporters can, however, still make one-off donations to a closed project.