If you want to submit a URL for indexation just inspect the specific address using the search bar at the top of your GSC account. When reviewing the inspection results you will see an option to index the page if it is not already indexed.
From the screenshot it looks like you're trying to add a new property, not fetch a page from an existing property. Have you been verified as an owner or been delegated full access to GSC for the site you're looking to work with?
The blog you are trying to index is a HTTPS url and you are looking an HTTP version of the domain. In Google's eyes your HTTP and HTTPS versions of your site are separate properties.
You need to verify the HTTPS version of your site and index it from there.