How Respawn Players in Multiplayer Mode?

I really have a hard time to make respawn system in multiplayer mode and reset player setting and variables?and where this Blueprint should be?

Take a look at the multiplayer shootout project from Epic. It goes over how to spawn players and resetting variables back to start.

You would put the code to spawn or respawn your character in your game mode, or some people do it in your player controller. Either is okay so long as the event is handled by the server and has authority.

Check out this documentation on online multiplayer.