The Deal Source List component displays key information about Deal Sources. By default, certain field values (Name, Capital Source, Account, and Contact) are copied from Deal Sources to the Deal Sources grid while using the Copy From functionality. If you'd like to extend this list and include additional fields, follow the steps below. 
Step 1: Navigate to the Object Manager: 
1.In Salesforce, go to Setup by clicking the gear icon in the top-right corner). 
2.Under the Quick Find search box, type Object Manager and select it. 
3.Scroll down and select Deal Source from the list of objects. 

Step 2: Create a New Field Set: 
1.Inside the Deal Source object, look for the Field Sets section on the left side. 
2.Click on Field Sets to view and manage existing field sets. 
3.Click New to create a new field set. 

4.In the Field Set Name field, enter the name CopyFromFields (this is the required API name). 

5.Save the new field set. 
Step 3: Add Fields to the Field Set 
1.After creating the field set, you’ll be prompted to add fields to it. 
2.From the available fields list, select the fields you want to populate value from the selected Deal Sources. 
3.Add the fields by dragging them to the Selected Fields list.

4.Once the necessary fields are added, click Save to apply the changes. 
With these steps, you’ve successfully extended the list of fields that are copied into the Deal Source grid while using the Copy From functionality.