The picture bellow helps with the visualization of the end result. We have to override the default value-prompt item with the value of the current month.
To achieve the result just follow the steps:
Add a Value Prompt control and connect to a data item to return the months;
In Properties, set Static Choice property as: Use: MDX code to return the current month Display: Some description that will be visible to the end user;
Values used in this example: Use: linkMember(item(members([ECS Cube].[Tempo].[Current Month].[Mês]);0);[ECS Cube].[Tempo].[Tempo].[Mês]) Display: Actual.
Tip1: linkMember function is compatible just with Cognos Cubes;
Tip2: The MDX code has to return a member from the same hierarchy added in the data item.
To ensure that the Static Choice value be selected by default, set Default Selections Property with the same MDX code used in Static Choice.