Procedure
Go to Map > Trips History.
Open the Options drop-down box.
Configure your options as required and toggle the Trip Categories section to Show All > Apply Changes.
Find the trip you need to change, click on the 3 dots to the right of the trip:
Select Change Category and choose the new category for your trip, add an annotation > click Save
Additional Notes
Categorize and add annotations to trips feature preview will need to be ON for you to make this change. To learn how to enable/disable feature preview, see the How to turn off Feature Preview community article.