The change can be made through the desktop site by using the Edit All button on the related list of products on the opportunity page. This button allows you to edit multiple products at once and change their price book entries. You cannot use this button on the mobile app, as it is not supported. You also cannot change the price book on the opportunity once it has products added to it, unless you remove all the products first. References: https://help.salesforce.com/s/articleView?id=sf.opportunity_products_edit.htm &type=5 https://help.salesforce.com/s/articleView?id=sf.opportunity_products_change_pricebook.htm &type=5