If you already have Medicare Part A and wish to sign up for Medicare Part B, print the following two forms and take or mail them to your local Social Security office. You can also call Social Security’s toll-free number 1-800-772-1213 (TTY 1-800-325-0778). or contact your local social security office from the link given above. If you are already enrolled in Medicare Part A and have chosen to delay enrollment in Medicare Part B, you must complete the additional forms (listed below). Link 40B form: This allows you to apply for enrollment into Medicare Part B only. The 40B form must be included in your online application or mailed directly to the Social Security office. Link L564 form: Your employer must complete this form if you delayed Medicare Part B due to creditable group coverage through said employer. You must also include the completed L564 form in your online application, or mail it directly to the Social Security office