You can add a particular contact in a group by following the steps below.

• Click on the drop-down at the top right tool-bar.

• Click on "Contacts" at the drop-box.

• Click on "+Add contact" present at the top second button from left.
• This will give you a pop-up "Add contacts from".

• Select from the options on the pop-up.

• You will get a list of all the event members.

• Select contacts that you wish to add to a group.
• Click on "+Add to Groups".
• This will give you a pop-up "Add contact to group".

• Here you can select a particular group at the drop-down and click "Save Changes".

• This will add a specific contact to a group.