Hey, once you create a flow you can’t change the trigger (https://help.klaviyo.com/hc/en-us/articles/115002775052-Change-a-Flow-Trigger).

The best way would be to clone the flow and set up a new trigger based on the above link.  As for having more than one list to a flow, you won’t be able to do that either.  The way to get around that is to create a segment that includes multiple lists and then create a flow based on the segment (https://help.klaviyo.com/hc/en-us/articles/115005078887-Combine-Two-or-More-Lists-in-Klaviyo).  

Keep in mind your subscriber experience though, make sure they aren’t getting the same emails twice.  You can add custom properties to their profile to prevent that from happening (https://help.klaviyo.com/hc/en-us/articles/360049615712-How-to-Add-To-or-Combine-Lists-Without-Triggering-a-Flow)

Thank You Manny!