Click on the customization option on the top bar a left sidebar will appear with customizable options, you can see an edit icon on the logo click that edit icon and change the logo text and font awesome icon by font awesome codes.
If you want your logo as an Image, enable the Image logo required to go back to the customization and click site identity > select logo > and upload your logo image you can crop the image or skip cropping.
Now your image logo is ready click on the Publish button to save your changes.