Users can delete multiple comments at the same time for an issue. Plugin preserve the following permissions on the issues
Delete All Comments - Permission to delete any comments, regardless of who added them.
Delete Own Comments - Permission to delete comments that were added by the user.
Moreover, issue must be editable state to delete comments.
1. Select "Delete Comments" from More actions
User must have Delete All Comments or Delete Own Comments project permissions for selected issue's project to access/see Delete Comments action at More action list.
2. Select Comments to delete
If user has Delete All Comments project permissions for selected issue, s/he can select all comments.
If user has only Delete Own Comments project permissions for selected issue, s/he can only select own comments.