"Assigned duties" refers to tasks or responsibilities that are officially given to a person. It means that someone is given specific work or jobs to accomplish as part of their role or job description. Full definition
It is not uncommon for the accounting manager to supervise other accounts personnel and manage the unit to ensure timely completion of assigned duties with precision. (jobdescriptionandresumeexamples.com)
He / she should be a team leader and provide a helping hand to other members of staff in performing assigned duties; this encourages lower ranking staff and improves on their job performance. (jobdescriptionandresumeexamples.com)
Proven ability to adapt quickly, and finish assigned duties in a timely manner. (members.climber.com)