1. From Setup, click the Object Manager tab. SelectCases, and open the Buttons, Links, and Actions setup page.
2. Click New Action.
3. For Action Type, select Create a Record.
4. For Target Object, select Case Comment.
5. For Standard Label Type, select None. For Label, enterCase Comment. The Name field is auto-filled. Optionally, enter a description and success message.
6. Click Save.
7. To choose the fields users see, customize the action’s layout, and clickSave.Keep these things in mind.The Body field is always required, even if Required isn’t selected in its Field Properties dialog (invoked when you double-click the field).The Public field is available only if you have Communities enabled.The Public field is labeled “Published” in the quick action layout editor.
8. The Body field is always required, even if Required isn’t selected in its Field Properties dialog (invoked when you double-click the field).
9. The Public field is available only if you have Communities enabled.
10. The Public field is labeled “Published” in the quick action layout editor.
11. Go to the Case Page Layouts setup page, and edit your case layout.Drag the new quick action to the Salesforce Mobile and Lightning Experience Actions section, and click Save.