Grabbing the adds can be a chore since they scatter once they appear which will cause some annoyance with the raid if some escape.
Immediately after the right arm has been destroyed be sure to stand in the rubble then cast concentration. This will ensure the pack of earth elementals will get hit by your concentration when they appear. If you are a second or two late the elementals will scatter and attack the party.
FYI – You may need to compensate for your personal latency.
Once you have established control of the elementals, kite them to Kologarn’s body. Then any splash damage will hit the adds and eventually kill them. Also this will keep you safe from the eye beams and allow you to obtain the bosses aggro (if necessary).
When the right arm re-generates, ask the raid to kill the remaining adds (if any). Then help DPS then move into position once the right arm has been destroyed. Rinse and repeat.