ubuntu16.04 pip3 broken after upgrading - pip

Question

I am using Ubuntu 16.04 to work. There is a need from my work to upgrade pip.
I was using the command:
pip3 install --upgrade pip
After that, every time I call the command pip3 will get the same error:
File "/usr/bin/pip3", line 11, in <module>
sys.exit(main())
File "/home/my_user/.local/lib/python3.5/site-packages/pip/__init__.py", line 11, in main
from pip._internal.utils.entrypoints import _wrapper
File "/home/my_user/.local/lib/python3.5/site-packages/pip/_internal/utils/entrypoints.py", line 4, in <module>
from pip._internal.cli.main import main
File "/home/my_user/.local/lib/python3.5/site-packages/pip/_internal/cli/main.py", line 57
sys.stderr.write(f"ERROR: {exc}")
^
I've tried to search solution by myself and followed this to try to deal with the issue.
This is the command I tried:
curl -fsSL -o- https://bootstrap.pypa.io/pip/3.5/get-pip.py | python3
However, after I tried the command, I got another issue:
Traceback (most recent call last):
File "<stdin>", line 23974, in <module>
File "<stdin>", line 199, in main
File "<stdin>", line 121, in bootstrap
File "/home/my_user/.local/lib/python3.5/site-packages/setuptools/__init__.py", line 18, in <module>
from setuptools.dist import Distribution
File "/home/my_user/.local/lib/python3.5/site-packages/setuptools/dist.py", line 585
license_files: Optional[List[str]] = self.metadata.license_files
^
SyntaxError: invalid syntax
Is there any other way to fix this issue except remove and install python3.5 again? because the python3.5 is used in the Ubuntu 16.04 OS, if I remove it the system will break.
Thank you very much.