What should I say in my cover letter if I was fired from work?

If you were fired from work, you do not need to bring up that you were released when you create a cover letter in the future. Your cover letter is simply a document that you can use to introduce yourself to potential employers and you do not need to get into the details about your last assignment. In your cover letter, you only want to highlight the good things about your skills and experience. This is not an area to mention being fired. When you are interview, if the employer asks about it, then you can address the issue.