New and need help with the Chester step method

Hi, I'm new to the site and could do with some advice if possible.

I performed the Chester step test today as part of the enrolment process for the fire service but only achieved a score of 38. I needed a score of at least 42 to qualify.

I have been given the opportunity to re-sit the test in a week. Is it possible to raise my score this much in this period of time?

The instructor said that as I was just getting over a cold it may of affected the result, and he advised me to increase my exercise over the next week.

I usually attend British Military Fitness twice a week or run 3 miles however I was unable to do this last week due to illness.

I would like some advice on what would be the best type of exercise to do this week and whether realistically I can improve this much.

Thanks,
Matt