Here are some quotes that I find on the official Microsoft website , which I think might help:
For site administrators
This problem occurs because the directory browsing feature is not enabled on the website and the document is not configured by default. To resolve this issue, use one of the following methods:
Method 1: Enable Directory Browsing in IIS (Recommended)
To resolve this issue, follow these steps: Start IIS Manager. To do this, click Start, click Run, type inetmgr.exe, and then click OK. In IIS Manager, expand the server name, expand the Web sites, and click the website that you want to change. In the Features view, double-click Directory View. In the Actions panel, click Enable.
Method 2. Add a default document
To resolve this issue, follow these steps: Start IIS Manager. To do this, click Start, click Run, type inetmgr.exe, and then click OK. In IIS Manager, expand the server name, expand the Web sites, and click the website that you want to change. In the Features view, double-click the default Document Default. In the Actions panel, click Enable. In the File Name box, enter a default document name and click OK.
Method 3: Enable Directory Browsing in IIS Express
Note. This method is intended for web developers who encounter a problem when using IIS Express.
To do this, follow these steps: Open a command prompt and navigate to the IIS Express folder on your computer. For example, go to the following folder on the command line: C: \ Program Files \ IIS Express Type the following command and press Enter: appcmd set config / section: directoryBrowse / enabled: true