You must write to the service center where you file your tax return, Attn: Entity Section, and ask for IRS letter 147C, "EIN Previously Assigned" . If you have it, yiou must enlcose a copy of the Second "B" Notice with your request. If you do not have a "B" notice, then enclude a cover letter stating the circumstances.
BWH regulations require that a payee request letter 147C in writing. Acceptable written requests may be received by IRS personnel via United States Postal Service or by fax.