First, you will need he terrain the mission runs on. Put that terrain.res file in the ahiiter folder.
Next, take the mission.res file, and put it in your missres folder.
Now, boot the game, select the terrain the missin uses, hit offline arenas, go to practic missions, select the mission, and hit "select".
Note that mission that use a warp point no longer work in this current version. Seems like HTC breaks the missions for the longest time, fixes them, then breaks them for a very long time again.