You can change the assigned agent of a contact so that the correct agent will be notified of all contact activity.
Go to the Contacts tab and find the contact that you want to change the assigned agent for.
If the contact is Unassigned to any agent, click +Assign and choose the new agent from the dropdown menu.
The contact will now be assigned to the agent that you chose. If you want to change the contacts assigned agent, proceed to Step 3.
Click on the agent profile circle.
You will enter the contact page with details specific for that particular contact. On the left, click the currently assigned agent.
Choose the assigned agent from the dropdown menu.
The contact will now be assigned to the agent that you chose.
To learn how to change the assigned agent of multiple contacts at once, check out this article.