The error message
No module named 'prettytable'
means the module is not installed for your Python. You can only import a module that's installed. A module can be installed by Python default (that's called built-in modules), or explicitly by yourself, or when you install another module.
To install prettytable for your conda environment,
run conda install -c conda-forge prettytable
from your terminal (command line). Then you will see a bunch of command line instructions. Read carefully, and hit 'y' when you are asked to proceed. If the installation is successful, the process will end with some lines like
Downloading and Extracting Packages
prettytable-0.7.2 | 14 KB | ##################################### | 100%
Preparing transaction: done
Verifying transaction: done
Executing transaction: done
Then you open python (or Jupyter or whatever you use to run python) and try import prettytable
again.