There seems to be an increased level of interest in Amateur Radio at DMS. The application to take an exam requires that you list your Social Security Number or FCC Registration Number (FRN). The best option to submit a request online for an FRN and use that on your application. It is free and, I think, issued immediately when you apply. Use the following link. It requires your SSN but you are working with an fcc.gov site.
If you already have a ham license, you have an FRN. To see it use the following link to display your license info.
I hope to see you at Ham-Com 2019 on Friday or Saturday.