How to add my own module to dask worker env to avoid no module named

I use dask clusters to process dataset. My dask python project structure is as follows:

project_name/
  folder_a
    a.py
  folder_b
    b.py

I import function function_a() within a.py in b.py like follows:

from folder_a.a import function_a

@delayed
def test(input_str):
  return function_a(input_str)

client = ...

d_task = [test(str)]
dask.compute(d_task)

However, dask worker nodes throw exception ModuleNotFoundError: No module named 'folder_a'

I have tried many solutions like add PYTHONPATH={dir}/project_name while none of them are available.

How to solve this problem? Is there any way that can add {dir}/project_name to dask worker environment?