If the group assignment was set up to assign grades to each student individually, the submission will still apply for each group member's assignment, but the drop-down menu displays the name of each individual student [1].
When grading the submission [2], the entered grade will only apply for the student whose submission you are viewing.
Individually graded group assignments include commenting options. To send your comment to one student in a group, select Send comment to this student only [3]. To send your comment to the whole group, select Send comment to the whole group [4].
Individual comments also appear in the Submission Comments filter in Conversations.