Hi, my name is Kelly, and I'm an independent consultant and I'm here to help.
To reset the Microsoft Authenticator app for your lost device, you will need to follow these steps:
Go to the security settings of your Microsoft account, either on a web browser or on a different device.
Click on the "Security info" option and sign in to your account.
Under the "Security info" section, locate the "Authenticator app" and click on "Manage".
Click on the "Remove" option next to the lost device. This will remove the Authenticator app from the lost device.
Set up the Microsoft Authenticator app on a new device by downloading and installing the app on your new device and then following the prompts to set up the app.
Once you have completed these steps, you should be able to use the Microsoft Authenticator app on your new device. If you have any issues during the process, you can contact Microsoft support for further assistance.