There are at least two ways to approach this question.
First, it is possible to approach it as if you are a worker and must reduce your own levels of stress at work. Here, the approaches you could take would vary to some degree with what is stressing you. For example, if you are having stressful relations with a coworker, you might ask a supervisor to help mediate between the two of you. As another example, you might try to organize your work better if you are getting stressed by that. You might keep better track of what needs to be done, by when, and what stage of the process of completing the work you are in.
Second, it is possible to approach this as if you are a supervisor and must reduce other people’s stress levels. Here, the best thing that you can do is to make work as predictable as possible for your employees. You need to let them know as much as possible what is to be expected of them. It is generally stressful to workers to have expectations and responsibilities change without much notice. Therefore, you can reduce their stress by making it as easy as possible to predict what is going to happen on a given workday.