This session is all about swimming above your race pace.
A good warm up is followed by a short kick set, on your side changing after every breath. Please make sure you don't move your head when you move your body and don't move your body when you move your head. Then swimming with a band around your ankles, trying to keep your lower body close to the surface of the water, pushing your chest into the water and using your core to raise your legs. Followed by the Finger Drag drill.
The set of 6 sprints followed by a length of recovery should be done at your maximum speed on the sprint length. The aim is to help you flush lactate, so even consider doing Fly on the sprint length if you can maintain a good fly stroke.
Next, the main set is all about pacing. Keep the same pace on all the swims and take 10s rest between each. That makes a split 400m swim, where your nett time should be faster than your normal race paced 400m. Take the recovery and then repeat for a useful fast paced set.