Hi, yes, I answered this a few months ago when I came across the same wall. I used the Open Level node (upon clicking on a menu button for a certain mode) to load the desired level and added this as a parameter in the options input of the node. You would change ThirdPersonGameMode.ThirdPersonGameMode_C to whichever game mode you want. Keep in mind to add the _C to the end, even if you don’t see that in the name of your game mode in the file explorer.
?Game=/Game/Player/Blueprints/ThirdPersonGameMode.ThirdPersonGameMode_C