If your TTP account (which is not your your NEXUS membership) is suspended, then you can call 855-873-4637 from the United States, or 202-325-8060 from Canada. They will reset your password for you.
If your NEXUS Card has indeed been suspended, that is another matter entirely. You should have received some kind of written notice about this. And that notice will tell you why you were suspended (roughly) and you can then look into appealing. Learn more here.