MultiLine Messages View can be added to Contacts, Leads, and Person Account Records Page.
- Click in the tab area
- Click Add Tab
- Name the tab as MultiLine
- Locate MultiLine Messages List View under Lightning Components on the left section
- Drag it under the MultiLine tab
- Click Save
- Click Activate
- Click App Default. Then Assign as App Default
- Select desired Lightning apps and click Next and Save.
Repeat the steps above for the other Lead and Person Account pages as well.