Some people get worse as cold and exercise trigger attacks. Most improve due to an increase in the body’s own steroids and reduced airborne allergens.
Carry all your inhalers at all times.
Prevent problems by reducing activity, taking medication and descend if needed.
Avoid anti-inflammatory drugs (like aspirin and ibuprofen).
Do not go unless your asthma is stable.
Ensure you are up to date with travel vaccinations and consider flu vaccine.
Include spare inhalers / spacers and steroids.
Know triggers for your asthma and try to avoid these on your trip.
Build up training, starting at lower altitudes and lower levels of exertion.