On the site, https://www.kunstmuehle-veckenstedt.com/en/anfahrt/, you will find how to get to the Art Mill.
The Mill of Arts is easily accessible by train, bus or BlablaCar.
Nearest villages are Ilsenburg, Stapelburg or Wernigerode.
Here you will find more travel information.
Timetable for Veckenstedt bus station (search for Veckenstedt Busbahnhof) The bus station is only a 5 minutes walk to the mill.