Customize the Help Menu

  1. If you’re not already in Setup, click Setup and select Setup.
  2. In Quick Find, enter help, and then select Help Menu.
  3. In the Section Title Label field, enter Label. Salesforce recommends naming the section so users understand that the resources are custom help for your org or company. Labels appear as you’ve entered them; they are not translated.
  4. Add a custom resource:
    1. In the Label field, enter Label.
    2. In the URL field, enter URL. You can add up to 15 resources. Items are listed in the Help Menu in the order that they appear on the setup page.
  5. Save your changes.
  6. Turn on Customize the Help Menu.

Reference:https://help.salesforce.com/articleView?id=customhelp_lexhelpmenu.htm&language=en_US