From today, it is possible to submit documents related to the DER by identifying yourself with the CSV of the document without needing to have a NIF.
 
You can check the procedure through the following route on the AEAT website: 

Home > Travelers, posted workers and cross-border workers > VAT refunds for traveler purchases (DIVA) > Featured procedures > All procedures > Respond to requests, submit claims and/or provide documents or supporting evidence

 
It will be necessary to complete the DER CSV (TAX FREE FORM) that appears at the end of the document. Using this procedure involves submitting a communication that will be processed by the competent bodies in a timely manner. "