After recording, finishing, and syncing an activity, you can still edit it from the mobile app
First, open the activity by tapping the activity you wish to edit from your Feed. Then tap the Menu button - the three dots - at the top-right of the activity page (highlighted below) and select Edit Activity.
You will then be taken to the Edit Activity page, from which you can add an activity title, change the activity type, add any tags, add a description, change your Gear, or change your privacy controls. Tap 'Update Activity' to save any changes you make or tap Cancel to discard your changes.
If you wish to Delete your activity, follow the same steps as above, but select the option to 'Delete'. Note that activities deleted from the mobile app are permanently deleted from your account.