Hope this helps to someone since I was not able to find this easily. When you need to define which columns will be shown in the Add Opportunity Product Page, you to do as follows:

1. Setup | Object Manager
2. Find the Price Book object
3. Click on Search Layouts.
4. Click on the Edit opcion



5. Set the fields you want to show as part of the Selected fields column.
6. Finally click on the "Save" button and you are done!



Remember to comment of like it if this helped you.

Regards
Jose Navarro

We have been using Survey Force free app which was provided by Salesforce labs. We would like to understand if this app is lightning ready?