If you'd like to sell this house, first try to cover up that smell. (Note the comma after "house")
No, it's not adjectival, it's the main part of the sentence which you can call the main clause. In advanced grammar, it's called the 'apodosis'.
The subordinate clause "If you’d like to sell this house" is a conditional clause called an 'adjunct'. Adjuncts like this don't modify anything; they simply express conditions under which the main part of the sentence holds.
In your example, your trying to cover up that smell is conditional upon your wanting to sell this house.
You are correct that "you" is the understood subject of "try".