I have a nintex workflow that is used across multiple sites that when a new item is created in a list of one of the subsites it creates a new item in the master list at the root of the site collection.  The problem is, when the item is edited at the subsite it creates a brand new item in the master list but what I need it to do is copy over the original. 

The workflow goes like this:

Run If: 

Condition - If any value equals value, Value "Update" is not empty

Create item in another site:

Site URL, List Name, Content Type - Item, Value - "Project Name", Value - "Update", List Lookup - "Week Ending".

The settings for the workflow are:

Start when new item is created and Start when items are modified.

This works exactly the way I wanted it too except  when the user at the subsite level edits an item in that list it creates a 2nd line item in the master list instead of copying over the first.

Can anyone tell me how I could prevent creating a new item and just copy over the first?