Use a max repel, make sure the Pokemon in the first slot in your team is under level 75, and run around in the grass in Ten Carat Hills' farthest hollow until Necrozma shows up.
Make sure after you met and answered the elder, you find the eighth gym leader (Clair) to collect the TM. After collecting the TM, go back to meet the elder...
Actually, the "Something went wrong" message pertains to a network or system error. Try resetting your Xbox One by turning it off, waiting for a minute, and then holding down...