To enable the integration with Miro, go to Settings → Integrations page, find Miro and click + Add.
Close the Settings page and try to create a new Miro board using +Create button in the bottom left corner. Click Select Board button and sign up into Miro account. Once you are authorized, you will be able to pick up an existing Miro board, or to create a new one.
For more information check the detailed article on Miro integration.