You can submit feedback on a machine after you have spent 3 hours on the machine, or you have submitted the relevant hashes for that machine.  When the time duration has reached the 3 hour limit or you have submitted the hashes, the more command drop down menu will show Feedback in dark color.  At this point, you can submit feedback on the machine.

1.  You can access notes by clicking on the three vertical dots (More Command) menu located on the far right of the lab machine row.

2.  Click on Feedback in the drop down menu.