If you use the eBay app, you should be able to do this. Check under Customize in the Filter menu to see if "Lockable Filters" is enabled. Sometimes an update to an app can alter the settings, and those settings may need to be restored.
Then search and select an item location filter option and you should see a lock icon appear. Tap the lock icon so it turns blue and locks to set that as your default search option. From then, all your searches should include that filter option until you unlock or change it.
