Hello. I am trying to figure out how to edit or create new Lightning Experience Action/Button/Links. The out of the box fields in the Task that are available to choose from need to be edited or changed to something new. 

Object>Page Layout>Salesforce Mobile and Lightning Experience Actions

How do I add Actions to choose from for this section of page layout and can I edit what fields are in those actions? For example Log A Call needs different fields under that action. That Log a Call action is under the Activity Action Tab. How would I edit the fields within that particular action?

Any help is appreciated! Thank you!