Change Julia version in Python through PyCall

I want to use julia package in python environment through PyCall.
I have two julia version in atom: v1.6 and v1.8. First installed PyCall in v1.6, and add"PyCall"), I could use the julia v1.6 package in python through import julia and julia.install().
But when I change julia v1.8, also set the same parameters, the packages that could be used still were julia v1.6.
How I can change it to julia v1.8 in python? my python is 3.7.

Thank you for your reply.