Ok. I have a list of Asset Items. I want to write a workflow to send out an email when the item's warranty will expire within 30 days. I know that when I write the workflow it is triggered either manually or when and items is created or modified. Besides going to each item in the list how can I apply the workflow to items that are already in the list?
There is no OTB support for your requirement. However there is a possibile with a work around by making the items updated with a small technique.
Here are the articles explains the technique to achieve your goal.