To change which camera is used when the game begins or stop the player being able to switch camera view go to the BP_CharacterComponent then click the Class Defaults button and in the Details panel search for camera.

Camera View – This controls the camera the player character uses when the game begins.

Allow Camera Toggle – If true the player can switch camera view, if false the player will not be able to switch camera view. The default key bind is V to switch camera view.