Ah, the gift of a challenge life hands us from time to time. As an active duty Marine I concur with Greg’s recommendation. I would also add that since being negative is partially attributed to muscle density, I would look to trim that and and increase cardiovascular stamina to the highest level possible prior to the test. Most instructors will work with you on the timing of this. I don’t know how old this person is but for what it’s worth I did it at 43 and I’ve been blown up, a lot. You can do this.