The key event window determines how far back in time an event is eligible for attribution credit. For example, if you have a key event window of 30 days, after a customer clicks on your organic products, any transaction that happens on your website by that customer in the next 30 days will count as a purchase in your Merchant Center reporting. Changes to the key event window only affect how purchases are counted from that point on.
To update the key event window:
- In your Merchant Center account, click Settings 
in the left navigation menu.
 - Select General.
 - Click Key event setup tab.
 - For website purchases,
    
- Click on the name of the key event that you would like to change.
 - Select a lookback window of 7, 30, 40 days. 40 days is the recommended lookback window.
 
 - For Google analytics conversions, [UA] Update your Attribution project settings [Legacy].
 - Click Save.