Compare CSV file to Sharepoint List, and add conditions

Hi Team,

I am learning how to use Power automate and currently struggling with this:

My current flow is building to created or update items in a Sharepoint list compare to a CSV file. If the item already exist, then "Update", if it doesn't exist, then "Create".

I would like to insert another condition : If one item exist in the Sharepoitn list but doesn't in the CSV file, then "update" it. I know I have to add ID of the Sharepoint item (likely in an array variable) somewhere in the flow and add a condition at the end of the flow, but I tried different ways and cannot succeed. 

Do you have any idea?

Many thanks