Trail Maps to Garmin 67i

Like Dave mentions you can download an AllTrails route to your computer (or phone) and either copy the file to the GPSMAP (GPX file goes into the Garmin\GPX folder, FIT course file goes into the Garmin\Courses folder) or import it in Garmin Explore app on your phone. Note the download option is only available on the AllTrails website, not in the app.

But if you have the  AllTrails+ subscription there's another option, which is easier imho, and that is to connect your AllTrails account to your Garmin Connect account. See https://support.alltrails.com/hc/en-us/articles/360019246271-How-to-link-your-Garmin-Connect-account-to-AllTrails and https://support.alltrails.com/hc/en-us/articles/15728433929620-How-to-send-AllTrails-routes-to-Garmin-Connect.

Note that you cannot download the actual maps that AllTrails uses to your GPSMAP, only routes can be transferred.