There are two ways you can access your extension's (i.e. form, shared view or portal) configuration:
From the extension's URL (what you would send to your end users), click Edit Extension in the admin toolbar at the top. This will open up the configuration in a modal (popup) so you can make adjustments, as needed. You can also navigate back to the miniExtensions dashboard this way. If you open a child form (by clicking on a linked record), there will be an Edit Form button in the child form's header, which would open that child form's configuration. This is a great way of navigating to exactly where you need to be in the configuration!
Find the extension on your miniExtensions dashboard, by navigating to the correct base and then selecting the extension.