How can I access the space administration menu when the sidebar is hidden?

In version 3.1.0, administrators can make the space tools link appear in the admin menu.

First, navigate to confluence administration and click Configuration under the HideElements heading. Please note that only confluence administrators have access to this page. Space Administrators talk to your Confluence Admin about setting this up.

Toggle the configuration and click save. If at any point you want to remove the space tools link you can come back and change the configuration.