Please contact the manufacturer of the vehicle or your registration authority, who will inform you of the further requirements for issuing a new or replacement type approval.
Only the holder of the ABE (manufacturer of the vehicle or sole distributor) can issue a replacement under certain conditions. A certificate from the registration authority responsible for your place of residence must be submitted to this authority stating that, according to the documents of this registration authority, the operation of the vehicle has neither been prohibited due to technical defects, nor has the operating permit been withdrawn. The confirmation of an officially recognized expert that the presented vehicle still corresponds to the approved type is also sufficient.
If the manufacturer of the vehicle or the sole distributor no longer possesses any documentation and is therefore unable to issue a replacement, an individual expert opinion by an officially recognized expert is required before the vehicle can be put into service. The expert opinion must be submitted to the registration authority, which will note "Operating permit issued" on it.
Further information, especially for vehicles manufactured in the former GDR, can be found here.