Update Multiple list items using SharePoint Designer Workflow

Simply can not be done.

• Numerous limitations to the structure and flow of your workflow. Examples include not being able to update multiple items, or see if the value of a field has changed - see here for more details. Major limitation vs. Visual Studio approach
• You cannot loop. If you want to perform an action on say all items in a list or all child items for a parent, you simply cannot do it unless you know how to lookup each item in the list at design time and have an action for each of those items.