Leonard, Are you talking about a company sponsored retirement account? If so, you should contact the HR department of your current or former employer.
If you are asking how to find your company plan on the Brightscope site, just go to www.Brightscope.com, click on Research a Retirement Plan and type in the name of the plan in the popup box. It will then come up if Brightscope has information on it. For plans that are not listed, contact Brightscope from http://www.brightscope.com/contact/ If you are asking how to find the login site for your company plan, you should contact the Human Resources Dept. at your company.
Perhaps this article is helpful. http://www.brightscope.com/financial-planning/advice/article/24529/10-Ways-To-Find-An-Old-401K-Plan/