What are the best ways to address dissatisfied employees to improve their levels of productivity ?

From my previous experiences and observations: Managers along with the HR should spend time with each dissatisfied employee to understand the reason for dissatisfaction and to reach a feasible solution that would benefit both the Company and the Employee.
Once the employee feels heard and cared for by his/her employer, he/she will automatically improve productivity.

Counselling and taking special care will certainly fetch good results out of an employee.

Envolves them in training sessions and make them feel their importance to the firm. Generally provide moral support to them

Motivate and support as a Leader 

first of all need to find the root cause of their dissatisfaction,it could be salary related or the issues with the colleagues after all their dissatisfaction could affect their performance and it will result on the overall performance of the Branch.

The best way to address unhappy employees is to improve communication with them and adopt an open door policy , so that all problems and challenges can be handled quickly and correctly. In so doing, staff become more equipped to handle various situations going forward and develope their own brand of leadership when handling different sales and customer scenarios.