Hi @Vinod Kumar R 

The dropdown values come from the database so you need to manage that at the database level when it's a foreign key from another entity.

In your case, given the fact you're using a different data source with no relation to the Product entity you can add the following script on the Initialize event handler from the Grid block:

let flexGrid = OutSystems.GridAPI.GridManager.GetGridById($parameters.GridWidgetId).provider;

// Set the default value for the dropdown column in the initial data
flexGrid.itemsSource.items.forEach(function (item) {
    // If Score has no value
    if (item.Score == null || item.Score == undefined || item.Score === '') {
        // set the ID of the Score to set as default
        item.Score = 3; 
    }
  
});

Hope it helps!

Cheers,
GM