Do you have a resume with cover letter already made from the last job you applied for?
Crumple it up, and throw that generic cover letter for any resume out.
I’m interested in a the tier 2 help desk position at CodeGen Logistics because…
I’m interested in the opening at your company
You see, writing the best cover letter means to customize it for each job you apply to. You need to tailor your cover letter to the employer. Sure, there are going to be some parts from the last cover letter that you can reuse, but I’d say about 75% of it deserves to be redone.