Select the list. Then click the arrow next to Bullets in the Paragraph group of the Home tab. Choose Define New Bullet.
Click Symbol to select the appropriate check box symbol
Check the result
3.12.List | ||||
3.12.1. | Create a Bulleted List | |||
3.12.2. | Create a Numbered List | |||
3.12.3. | Create a numbered list by typing | |||
3.12.4. | Change Bullet or Number Styles | |||
3.12.5. | Create a Multi-Level Bulleted or Numbered List | |||
3.12.6. | Format the multi-level list | |||
3.12.7. | Defining a new list style | |||
3.12.8. | Creating a printed checklist |