Not sure if anyone has posted this yet but couldnt find anything
1. Enter your Mythic instance (BRH or VotW)
2. Kill first boss
3. Run out the instance with your group (do not reset, just run out and in)
4. Enter instance
5. Start Keystone
6. Group gets teleported infront of first boss in VotW or ontop of the first boss in BRH
Enjoy