Both are important.
The building, how it relates to surrounding landforms, how qi enters, etc. is strongest influence.
But the apartment, how qi enters, even the hallway leading to the door, is the most immediate influence.
Plot and study appropriate charts for both. See how the building feng shui influences the apartment's
From this you can make decisions about room use, furniture placement, etc.
Cures, well I have no faith in cures....
Don't despair. The situation may not be nearly as bad as you think.