Run on a flat path, track or treadmill. You can use the 8/2 method of 8 minutes running, 2 minutes walking. While running, run like a Kenyan - smooth and efficient. RPE should be light - 5/6 out of 10.
Swim 4 laps (8 lengths), and take a 1 minute break. Do this 5 more times for a total of 1200 yards.