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!
Some parts of the extension will also show a gear icon when hovering over it, which then takes you straight to the relevant configuration page in a popup (modal).
Find the extension on your miniExtensions dashboard, by navigating to the correct base and then selecting the extension.