My advice is to be honest with the company.
If your asthma han't been a problem for years, and you are well controlled on preventive medication, there should be no problem. If you have significant asthma that is not well controlled, you shouldn't be doing that job at the moment. If you are not honest with the company, and they later find out, they might have good grounds to dismiss you, regardless of how well your asthma is controlled.
Cheers,
BM