In order to use the included game mode on a custom map, add enemy spawner and play start anywhere, set the game mode (BP_GameMode_Waves is for waves like in the example map, BP_GameMode_Blank is for if you don’t want to use waves and make your own one instead, but keep the character and weapons).
That’s it!
No joke, just put where you start and where the enemies are coming from, select the game mode, done.
Check out the other tutorials:
FPS Game Starter Kit 