Hello there! As your question is related to looking for identification/information regarding military personnel, our Guide on Military Identification may be of use to you. It provides a number of different resources, including how to request service records from a number of national agencies around the world, as well as graphical aids to assist in deciphering rank, unit, and other forms of badges or insignia. While the users here may still be able to lend you more assistance, hopefully this will provide a good place to start!

So Hilfszollassistent was a Rank in the Zollgrenzschutzreserve (link is in german) or "customs and border protection reserve" which was as the name suggests the reserve of the customs agency, it was an NCO-Rank

They were used in germany and the occupied countries to secure the borders and combat smuggling.