First, make sure you have at least one Ethereum account created. Head over to this page for more informations about how to add a cryptoasset account in Ledger Live.
Now that you have added your Live App inside your local Ledger Live application and have added an Ethereum account click Open next to your local Live App name in the developer menu.
Click on Dev tools to open a browser-like developer tools window.
Finally, click on the Request account button in the Live App, this will open a dialog box inside of Ledger Live inviting you to select an account.
Once you have selected an account, the associated account’s informations are displayed in the developer tools window that you previously opened.