To start using the Yealink WF40 Wi-Fi dongle, follow the steps below to proceed:

Disconnect the Ethernet cable to enable Wi-Fi connectivity.
Insert the WF40 USB dongle into the USB port at the back of the phone.
You will be prompted to scan and connect to available Wi-Fi networks. Alternatively, you can do this manually by going to 
Menu
 > 
Settings
 > 
Basic Settings
 > 
Wi-Fi
.
Select 
Available Networks
, and press 
OK
.
Select the desired Wi-Fi network and press 
Connect
.
Enter the password, and press 
OK
.