Não estou encontrando o aplicativo DGO para baixar no Roku express.

Where are you located?  Not all channels/apps are available in all regions.  What's the model number displayed under Settings->System->About?  Not all channels/apps are available on all devices.

If you've created a Roku account that is not in your region (e.g., you created a US account and are trying to use it in Latin America), many things won't work properly.