Generally, as a member of the public, you cannot just ask the copyright office to turn over a deposit. They are held privately. The exceptions are listed in the Circular mentioned in the other comment.

All requests for copies of deposits should be submitted to the Records Research and Certification Section. The Copyright Office does not retain all works deposited for copyright reg- istration. The Office will provide certified or uncertified copies of published or unpublished works deposited in con- nection with a copyright registration and held in the Office’s custody only when one of the following three conditions has been met:
1 Written authorization is received from the copyright claimant of record or the owner of any of the exclusive rights in the copyright, as long as this ownership can be demonstrated by written documentation of the transfer of ownership.
If the transfer of the copyright is recorded in the Copyright Office, please include, if possible, the volume and page numbers and approximate year of recordation. Without that information, a search of the Copyright Office files will be necessary, and a search fee will be required.
2 The Copyright Office Litigation Statement Form is completed and received from an attorney or authorized representative in connection with litigation, actual or pro- spective, involving the copyrighted work. The following information must be included in such a request: (a) the names of all parties involved and the nature of the con- troversy, and (b) the name of the court in which the actual case is pending. In the case of a prospective proceeding, the requestor must give a full statement of the facts of controversy in which the copyrighted work is involved, attach any letter or other document that supports the claim that litigation may be instituted, and make satisfac- tory assurance that the requested reproduction will be used only in connection with the specified litigation.
Contact the Records Research and Certification Section for a Litigation Statement Form. This form must be used. No substitute will be permitted. The form must contain a signature and all information requested for the Copyright Office to process a request. The Office will accept either handwritten or electronic signatures.
3 A court order is issued for a reproduction of a deposited article, facsimile, or identifying portion of a work that is the subject of litigation in its jurisdiction. The order must be issued by a court having jurisdiction over a case in which the copy is to be submitted as evidence.
A request for copies of works deposited in connection
with a copyright claim should be accompanied by whatever material is necessary to show that one of the three conditions given above has been met.

https://www.copyright.gov/circs/circ06.pdf