Auto assign task/follow up to individual sales?

Is there a way when a task formed itself from sequence followup; that it assign to one of our team member automatically? Is there a way to do that, or must be done manually?

Have you looked at your round robin settings or do you have different criteria you wish to follow?

It can be done automatically. You can use “Assign an Owner” in the sequence or you can do it by round robin or other means when creating the opportunity, as mentioned above. For a task, you can also assign it to the contact’s owner or to a backup if there is no owner assigned.