For Firewall/Appliance Setting the SSLVPN instruction, please click here to follow official instruction.
https://www.sonicwall.com/support/knowledge-base/170505401898786/

First you need ask the IT Administrator to get the following information:

  1. Link and IP address for SSLVPN access
    e.g. https://203.80.247.11  or  https://203.80.247.11/sslvpnLogin.html
  2. Username and Password
  3. Server Address
    e.g. 203.80.247.11:4433

Step 1: Goto the SSLVPN site

just type username, password and click connect

Step 2: Download the VPN client

click “Here” to download VPN client and install it

Step 3: After Install open the NetExtender and connect the VPN

type the server address, username and password then click “Connect”

if you got username and password incorrect, please make sure the server address is correct such as no missing “:4433

Step 4: Pop-up Security Alert, click “Always Trust”

Step 5: After connecting the “NetExtender” icon will change to blue, if disconnect will change to grey.