Bran and Meera are very close to Castle Black, thanks to the undead Uncle Benjen.
Benjen, who was revealed on season six to be "alive" thanks to the Children of the Forest, told Bran that he cannot pass beneath the Wall due to the magic keeping him in a state of undead/dead. But he told Bran he would continue to fight beyond the Wall in whatever way he could.
Bran and Meera are trying to get south to warn people about the Night King and the coming threat. Now that the Three-Eyed Raven is dead, Bran is the new Three-Eyed Raven.