Citation:

REAL3D. Real3d VolViCon [Software]. Version 4.2.0726. Aug 04, 2020. URL: https://real3d.pk/volvicon/

BibTeX:
@software{VolViCon,
  author = {{REAL3D}},
  title = {Real3d VolViCon},
  url = {https://real3d.pk/volvicon/},
  version = {4.2.0726},
  date = {2020-08-04},
}

Please change the publication date and version entries to match the software version you are using. From within the software, click Help | About to find the version information.