Hi Nelly 99
You have one month from the date on the decision letter to submit a Mandatory Reconsideration with any additional evidence. If you can't get medical letters or reports on time, put in your letter that you will send in further information as soon as you have it. If you can't meet the deadline at all, you have 13 months from the date on the decision letter to put in a 'late Mandatory Reconsideration'.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems