To manually map an activity, start with this article on how to manually post an activity. When you reach Step 2 you will see the option to manually plot a map.
After selecting Plot Map, click on the map where you want your start location to be, or search for your destination and begin plotting from there.
Zoom in or out if needed, and then proceed to click along the path you took during your activity.
If you’ve completed your activity on defined roadways, try selecting Snap to Roads in the upper left corner of the map. This will make it easier to plot your map.
After you've plotted your trip, you can link it to either a Route or a Race, before you select Next to enter the rest of your data.