Leads, Accounts, and Contacts already have the custom button for the Action Launcher available. Add the Action Launcher to these objects as follows:

1. Go to the Salesforce Setup.
2. Find the Object Manager and open it. 
3. Find the object where you want to add the Action Launcher and click to open it.
4. In the left-hand panel, click List View Button Layout.
5. Open or Edit the layout you want to edit. Usually this would be the List View layout.
6. Under Custom Buttons, you see Action Launcher listed. Select it, and add it to the Selected Buttons column.
7. Click Save.

The Action Launcher is now available in the list view of this object; either as a button in the top right-hand corner or as an option in the action menu there.