This only applies to trips you logged manually. If a trip was assigned to you by your outfitter, you won't be able to delete it yourself — reach out to your outfitter directly if you'd like to be removed from an assigned trip.
Steps to delete a manually logged trip
Go to your Trips tab or Calendar and tap the manually logged trip you want to delete.
At the bottom of the trip, tap More (the three-dot icon).
Select Delete.
When prompted, confirm that you want to delete the trip.
The trip will be removed from your calendar and trip list.
Curious how to create a manually logged trip instead? Learn how here.