You can predefined admin order comments under Sales > Dolphin - Predefined Order Comments  > Predefined Order Comments.

You can add predefined comments by clicking Add New Button from above address.

You can add content for predefined comments like as follows:

Title: You can add a comment title.

Content: Add content for comment.

Store view: Choose store view to display predefined comments.

Order Status: Choose order status for which you want to display comments.

Status: Choose Enable to display comment in dropdown for admin to select.

You can see all the predefined comments displayed in the grid.

Predefined comments grid includes following information:

ID: Id of the comment.

Title: Title of the comment.

Content: Content of the comment.

Store view: storeview on which the comments will be displayed.

Order Status: Order status for the comments.

Comment Status: Selected comment status. 

After creating some comments, you can see all the added comments under the Sales > Orders > Edit Order.

Exact above the default comment area under the Order Total section, you can see a drop-down for predefined admin order comments having all the comments you have created for the particular order’s status.

Select any one comment from the dropdown and you can see the comment area below to get filled up with the selected comment’s content.