To remove it completely from your computer you have to remove its services “Net extender” from the service page.
1) I am sharing with you its official article where they have explained how to remove Sonic Wall Net Extender completely from your computer. Please check out the article: https://www.sonicwall.com/en-us/support/knowledge-base/171210134226180
2) If the above step doesn’t work for you then remove it forcefully by using Revo Uninstaller or Geeks Uninstaller. Here’s an article to find out how to uninstall software forcefully from a computer
If it doesn’t work then let us know and I’ll give you more advanced steps. If it works, so please select my answer as solved answer.