Unfortunately, I don't know much about macOS. You will need to make sure the location of the Python 3 installation comes first in your PATH environment variable, before the Python 2 path. I'm sure there is a very user friendly way to do that, but I'm not sure what it is.
I see this:
You could go into that file and make sure to add the path of the Python 3 installation above the Python 2 one in the file.