How do you stop a maglev train?

The current flow is reversed in the opposite direction, which causes a retardation in the speed of the train.
MagLev trains use the rule that like poles of magnets repel to stop. So, the electromagnetic track just changes so that all the South and North poles all meet other South and North poles and the train is repelled, slowing it down. They balance it out, and the train is stopped.