The cover letter should comprehend two important points:

If that sounds like marketing a meaningless subject, consider that many marketing people miss that point. They spend time telling about their "great" product, when they really should be concentrating on telling how it will benefit the customer.

If you do not have some idea how you can benefit that customer, then you may be wasting everyone's time (including your own) in even attempting a reasonable job search. You will most definitely fail any interview. Go back to square one and start over.

Ask any smart marketing person the following question: “What is your company's competitive advantage in the marketplace?” If that person is competent, you will get a quick and ready answer. You should also have a prepared answer to the very same question. You need to certainly understand and be able to articulate your personal value proposition.

If you don't know what differentiates you from the rest of the market, find out! Investigate your background and make note of the areas where you transcend. And make that your number one focus in writing the cover letter.