Thanks for the reply.
For my character, there is no 7.0 quest on the command board.
I tried everything, almost completing all the critical quests in Broken Isles and completed the quest until “A Gift From the Six”.
Usually, the NPC for activating the 7.0 order hall will show up once the character gets to Dalaran automatically, but for my DH character, there is no such npc show to give me quest.