Cannot find some students while trying to assign them in pre-assigned breakout room

Cannot find some students while trying to assign them in pre-assigned breakout room

There could be two possibility:
A: Some may may not have NUS Zoom accounts yet.
B: Some could also be having NUS friendly email address; which Zoom uses if it's available. 

For those that cannot be added, ask them to Sign In to NUS Zoom at https://nus-sg.zoom.us. 
Guide to Sign In: https://wiki.nus.edu.sg/display/cit/Log+in+to+Zoom
Students should then provide you with the mail address in their NUS Zoom profile page: https://nus-sg.zoom.us/profile.