Recovery between rounds of 400m on the same day

Assuming the worst case scenario, with the athlete running near PB in the preliminary round in order to qualify for the final a couple of hours later.
What to do immediately after, in between and warming up for the second run. I’d like to hear your thoughts.

Warm down. Take a supplement stack (carbs, creatine etc) that helps with recovery from that kind of work (i have my own that i mix up - sorry personal secret!). You could also experiment with an ice bath. Do a shorter warm up for round 2 but get the blood flowing rather than a neural stim type thing.

Try using carbonated water between rounds

maltodrextrin, bcaa, glutamine, sodium bicarbonate (thoughts?), light self massage, contrast shower, micro stretching, …

and make sure that athlete won’t just lie on track after heats.
Make him walk around the track it’s alot better IMO