Follow the below steps to convert your one-on-one call into a group meeting:

• Click on the call button in your one-on-one chat window

• Select a preferred option to make an one-on-one audio/video call 

• During the call, click on the meatballs menu(3 dots) and select Add users

• Add participants by searching and selecting the users you want to add to the call
  

• Add the meeting topic
  

• Click on the Ring all button

• Once you have added users to the call, the selected participants will receive a ring to join the call