Since I can do this from online connection only, below is the method I could share with people.
Install-Module AzureADPreview
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser
Connect-AzureAD
$wytGroupName=Get-AzureADGroup -SearchString "input group name here"
$List = Import-CSV ".\userlist.csv"
ForEach ($User in $List)
{
$WyaUser=Get-AzureADUser -SearchString $User.UserPrincipalName
Add-AzureADGroupMember -ObjectId $wytGroupName.ObjectId -RefObjectId $WyaUser.ObjectId
}
Disconnect-AzureAD