Deleted List Warning Icon
A flow with this symbol next to the trigger will no longer function. Even if you delete the list and create another one with the same name, the flow's trigger will remain broken. The reason the flow is not deleted too is to preserve your analytics.
Clone a Flow
The best way to resolve this issue is to click Manage and then Clone Flow.
When you are prompted to create the cloned flow, you will have the opportunity to adjust the flow's trigger. Here, you can update the flow trigger to the correct existing list. Once you have configured this duplicate flow, you can go ahead and delete the original if you don't mind your analytics being deleted.