There are two key components to change a link for use with mobile devices:
1. Replace the http/https protocol at the beginning of the url with 'K2:'
Example instead of https://portal.k2.com/Runtime/Runtime/Form/ExampleForm/ you would drop the https: and use k2://portal.k2.com.
2. You will need to remove the 'Runtime/Runtime/' from the URL, so a final link that will prompt the user to open the item in the mobile app will look like: k2://portal.k2.com/Form/ExampleForm