You can reverse a trail route using either a desktop or laptop computer at AllTrails.com. This can only be done on our website and isn't yet available in the app. Once you've reversed a route and saved your map, you'll be able to find it in the app by tapping 'Saved' >> 'Lists' >> 'My maps.'
You'll first search for the trail you want to complete, then select the map image from any trail details page, to open the route. Once the map is opened, select the pen icon in the bottom right to open the map creator tool. The trail map will then be copied and displayed in the map creator tool, where you can customize it.
You can then click the overflow menu (3 dots) next to 'Route' and select 'Edit'. Then click 'Reverse' >> 'Save' >> 'Save custom map.' You'll then be able to access this map via the app by tapping 'Saved' >> 'Lists' >> 'My maps'.
This article has more details about how to create and customize maps.