No specific form is required. Your request must be in writing and contain the following information:
It must describe the basis for the claim and state the dollar amount you seek to receive;
It must include your name, address, and telephone number;
It must include the name, address, and telephone number of your current or last employer;
It must be signed by you; and
It must include any information you believe OPM should consider, such as cancelled checks or other evidence of amounts you paid.
Send your claim to: Office of Personnel Management, Retirement and Insurance Service, ATTN: FC Section, Washington, DC 20415-3200