If you need to extend the deadline of expired request, you can simply do it by changing end date of needed request. Just open the request on "General" tab and click edit icon near "End date". Select needed day/timing in the modal window, click "Apply" button and save entered information.
Then status of the request will be changed from "Ended/Pending" to "Running" and suppliers will be able to give their quotes. After you changed the dates the system will ask you if the supplier should be notified about those changes.