Yes, we do prepare the customs export declaration.
In case your German seller has not done it, we can do it. Additional costs for clarification 20,00 Euro plus 10,00 EUR per 1 customs tariff number.

What is a customs declaration?
It is needed for packages in non-EU countries only. When your shipment value is above 1000,00 EUR we need to do a certain declaration that requires customs involvement:
(https://www.dhl.de/en/express/versenden/hilfe-zollabwicklung/zollpapiere/ausfuhrbegleitdokument.html)
It means customs need to release the items which will take an additional day. But it also means we need the original invoices/proof of purchase for each item.

Customs Declaration and VAT Refund?
We will need to fill a form with the German customs (ATLAS) and will get a MRN number, which will be sent with your package. When customs in the destination country receive and conclude the MRN, then German customs will release the MRN and you can use that MRN for your seller as proof of shipment. Thus, he will be entitled to refund VAT (but not obligated).