Hi
I'm happy to let you know that a client of mine got himself off the DNR list by doing the following:
He was on Avis's DNR list. He wrote to their customer service department requesting that they delete all his details from the GDPR records. It took him two months to get a final confirmation that they had removed all information, but this past week, just two days following receipt of the deletion, he went to Avis in Frankfurt Airport and received a car without any problems.
Hope this helps anyone facing similar issues