The phrase "to write an assignment" means to create or complete a task that usually involves researching information and expressing thoughts or ideas on a given topic, often for school or work purposes. Full definition
Finding a topic for writing an assignment for college or university is the first and foremost challenge that students have to deal with. (studentsassignmenthelp.com)
Also, they have years of experience and knowledge in writing the assignment on time for the students. (studentsassignmenthelp.com)