Ok, there looks like multiple things going on at the same time.
First, you need to know what environment you are using. Two different environments do not share the installed packages.
So, let’s assume you have anaconda prompt on, and you have installed pymc with conda install pymc3 -c conda-forge
Then open python and run import pymc3. Does that work?
If that does, do the same with pystan (Don’t change environments or anything).