Click the "Startup" tab in the dialog that appears to display the programs set to run at startup. Scroll to the "Powershell Script" entry and click the check box in the file name.

This will cause Excel to display a dialog box that allows you to choose which items will appear on the ribbon. Select the Developer checkbox, shown in Figure 1, and click OK.

The dialog then prompts the visitor to install a "root certificate" by copying a PowerShell script into the Windows Clipboard and running it in a Windows PowerShell (Admin) console.