Relative imports are for use within packages. You could change what you have into one by adding some empty __init__.py files into your directory structure like this:
d1
 - test.py  # added to run script.py below
 - app
   - __init__.py  # an empty script
   — script.py
 - lib
   - __init__.py  # an empty script
   — lib1
     - __init__.py  # an empty script
     — file.py
There's also a new file I've called test.py because you genrally can't run modules within a package as the main script (which is why I added  test.py). All it contains is:
from app import script
I also changed the import in script.py to this:
from lib.lib1 import file
To show that the above import works, I put a print('in file.py') in file.py.
Now running test.py, which runs the script module by importing it, produces the following output:
in file.py
Now, if you want to import a particular function from file.py, you could do something like this in script.py:
from lib.lib1.file import my_func