Once you have collected 24 months of Social Security Disability Insurance benefits (including any retroactive benefits), you automatically become eligible for Medicare. Medicare becomes your primary medical coverage; your city coverage remains as secondary coverage.
Medicare charges a premium (currently ranging from $135.50 to $270.90, depending on your income) which is automatically deducted from your monthly benefit from Social Security. Medicare-eligible City retirees and dependents are eligible to have that premium reimbursed. Once you receive your Medicare card, you must notify the New York City Office of Labor Relations by providing a copy of your Medicare card and completing an application, available on the NYC OLR website: https://www1.nyc.gov/site/olr/health/retiree/health-retiree-medb-irmaa.page.
You only need to submit this application one time, once you are enrolled in the reimbursement program you should not have to refile every year. The reimbursement is usually made in each Spring; it is distributed in the same manner in which you receive your pension payments.