How to find out the initial name of a deep link from classmates?

Question

iOS

I want to make a deep link so that the user opens the application and does not go to the site. Other methods are of no interest.
Example:
https://vk.com/groupName -> vk://groupName
https://facebook/groupName -> fb://

groupName classmates, ok.ru, okru, ok, odnoklassniki - tried everything. I didn't find it in the doc. What are the secrets..