Be logged in; use the deletion link.
UPDATE: the direct link currently no longer works, yet is still available on their website. This might be temporarily. We’ve contacted Alltrails about this issue.
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.