If you want to store and name your waypoint flights you have to save them after you have created them. So if you created a waypoint mission in the park you could name it 'park'. Then when you want to access or fly saved waypoints (missions) you can find them in waypoint mode (under the name you gave it).
Soz but I misread your original post. I'm not sure werther or not you can rename the waypoint missions. If it's convenient maybe you could delete and re-fly the mission, then you could give it the name you want!
Come on! This is a core feature. I only have 4 saved waypoint favorites, and I cannot for the life of me figure out which one is which, without starting to fly, stopping, and trying the next one. Not being able to give them user-friendly names is STUPID. This would be a trivial feature to add, and it's inexcusable that the app does not allow it.