Below are the options available in Favicon, Search Engine.
Favicon image: Here you can set the favicon image that will be visible on the browser tab. Click on the Select favicon button and add the image by either uploading the image or selecting from the list.
This section will help you to improve the search engine ranking of your Under construction page.
Title: You can add the page title here.
Meta keywords: Add the meta keywords of your Under construction page here.
Meta description: Here you can add a meta description of the page within the <p>…</p> tags.
Google Analytics tracking code: If you wish to analyze the traffic or the audience of your Under Construction page, then you can add the Google Analytics tracking code here.
Facebook pixel: Here you can add Facebook pixel code which will help you to measure how effective your advertising campaigns are.
To know more in detail check it out from here.