To assign an executor, select the step to add an executor and you will see the properties window open adjacent to it.
Beneath the properties you will see the option to assign executors, click the plus to add in one or multiple executors.
You can select one executor or multiples to execute the task.
Furthermore, you may add conditions to trigger a specific executor, such as priority or department.
You can add multiple potential executors per step and you should ensure that any such conditions are correct.
It is important to remember that executors can be changed on a published workflow. However, should you wish to change the workflow, then you should create a new version (draft) of a flow.
You can utilise conditions and/or drag the priority executor above, if applicable.