You can try these things

Restart your PC. Then try again.
Try pip install mypy==0.910. Try again.
Check whether the location of the pip environment is specified in the Environment variables (Control Panel > System > Advanced System Settings >Environment Variables). If it is not add it or specify the path manually.

example -: mypy C:\<your file location>\hello.py
I have installed mypy via command prompt on Windows using this command line:
python -m pip install mypy, I'm using python 3.10.0, when I use pip list, it shows that  I have installed mypy 0.910 and mypy-extensions 0.4.3, but when I use it to check a program mypy hello.py, it said 'mypy' is not recognized as an internal or external command, operable program or batch file.. Can anyone help me with this? I don't know how to fix this problem. Thanks for your help!
Can't use mypy in command prompt for type checking in Python