Search Trailhead from the Help Menu
Review Trailhead search results right from the Help Menu inside the
app. Previously, only product documentation was available to search in the Help
Menu.
Where: This change applies to Lightning Experience in Group, Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: Click Search Salesforce Help and enter a search term.

Enter a search term to view both documentation and Trailhead search results.

When you open a Trailhead link in the search results, a new browser tab opens.