Answer:
Candidates for the job will make a good impression if they are knowledgeable about the company's products and services.
Step-by-step explanation:
They are talking about candidates, so how will i make a good impression if this is talking about the Candidates?
Candidates is a bunch of a people, so you can't use "you" as you are talking directly to one person, so you have to use "they" as it is used for a bunch of people.